VERY Concerning noise...

[PghMiller]

Yeah I know, it's tough to explain a noise... but I'll try anyways...

I've heard this noise ever since the first day I bought the car (1 year ago). It was faint and no one else heard it but me, so I wasn't too concerned. It almost sounded like the faint high-pitched screech of a brake sensor when your pads are starting to go bad (but that's not what it is). You could only hear it from the driver's side, and only when pressing on the gas pedal, and only around the 2000-2500rpm (just after that it disappeared). So just for the second or so, I would hear the faint screech. (during each gear shift)

Today I changed the stock air filter to the UniFilter, and now the sound is MUCH louder (passenger can hear it now) and lasts longer (from about 2000rpm to 4000 rpm). It's loud. Totally sounds like the brake sensor... but it's definitely not.
The sound isn't there if I'm just coasting... but when I press the gas pedal, you can hear it. And once I stop pressing the gas pedal, it stops.

I am now positive the sound is coming out of the driver's side air dam, where the air intake is. Now, even when the car is sitting idle, I can get out of the car and put my ear near the air dam and hear the constant faint quiet screech occurring in the engine (through the air dam). And when I had my wife hit the gas pedal a few times, the sound definitely is coming out of that air dam..... so it has something to do with the air intake or the engine itself and the sound is traveling through the air scoop.

ANYONE WANT TO VENTURE A GUESS??

 

[bngl3rt]

I have the exact same thing. Never noticed it before but became very pronounced as soon as I went to the UniFilter.

I opened up the airbox and took a poke around the engine bay but didn't see anything obvious so left it alone. It's not very concerning to me

 

[shawn110975]

well I seem to remeber a thread from a guy local to me posted about how the butterfly nut inside the manifold came off, unscrewed itself over years and was sucked into the engine or did some real damage to valves I forget but he described the same thing before it happened. worth a shot to inspect a little further inside.

my 2 cents.

now one last thing this was on another thread about making a noise similar to this and it was a small hole in one of the vacuum tubes that sound was air getting sucked in and guys we all know we never change them during normal hose replacements. mine is doing this sound but it had not done it for a long time now so I forgot about it till this thread.

any other thought guys? maybe the big LarryB can chime in

 

[JD Cross]

Could it be an alternator or A/C compressor belt slipping?

 

[PghMiller]

Could it be an alternator or A/C compressor belt slipping?

2 weeks ago I had all the belts changed and water pump, plus all the recommended gaskets, nuts, bolts, tensioners, etc recommended by Larry's write-up. Like I said the noise has always been present since I owned the car (1 year), it's just always been very quiet and barely noticeable... after the TB/WP job it still sounded very faint... but just today when I changed the air filter to UniFilter the noise got terribly louder!
Could I have done something wrong when performing the simple air filter replacement? All I did was remove 7 screws, unfasten those few hoses, remove cover, switch filters, replace cover and screws and hoses.

- - - Updated - - -

Could it be an alternator or A/C compressor belt slipping?

Something else that I found unusual... as I bent down and had my ear next to the air dam while my wife revved it up, I could clearly hear that the sound was coming through the scoop from the engine (or somewhere up there)... BUT when I stood up and leaned over to put my ear above the engine bay as she revved it, I couldn't hear it. I assume if it was a belt slipping it should be audible from the engine bay as well right??

This sound is a quiet high-pitched metal screeching/hissing sound (like the sound when your brake sensors are telling you to change your pads), ONLY when i'm pressing on the gas pedal.
But to be honest, if a tech discovered that the sound was actually an AIR/hissing sound, I wouldn't be surprised... because it kind of sounds like that too.

 

[JD Cross]

This may sound weird but my next suggestion is get an old stethoscope and start listening to the sounds from various areas of your engine bay.
You should be able to narrow down where your noise is coming from.
Old hot rodders used to do this to hear which lifter or con-rod was making all the racket.
It works

 

[jwmelvin]

But to be honest, if a tech discovered that the sound was actually an AIR/hissing sound, I wouldn't be surprised... because it kind of sounds like that too.

That is my thought. When I put a unifilter in my last car I noticed all sorts of hissing noises. I suspect you are hearing a normal noise.

Edit: When I drove to work this morning I definitely heard an intake sound that could be taken for metallic scraping. Am I correct that this is only under certain throttle positions? As in moderate throttle, whereas more or less makes the sound go away?

 

[Aluminsx]

So you've got some clues with regard to the noise in that it only happens when you press on the gas. I'm sitting here trying to think of what happens when you hit the gas and one of the things that jumps into my head is that the engine is trying to twist which puts a strain on motor mounts. This is just a shot in the dark but if you have a compromised motor mount and you're getting some high freq vibration I suppose it could sound like the noise you're describing.

 

[shawn110975]

could be Timing belt tensioner if you reused the old one it could make noise but it would be on the other side and not coming from the intake area

 

[Aluminsx]

I think the intake is just magnifying the sound coming from where ever it's coming from. Sorta like speaking through a mega phone.

 

[silver2002]

I used a digital recorder and a musicians microphone to track down a sound.
Move it all around engine/car/inside trunk/exhaust while saying where the mike is, then listen to recording.
Mine was a high pitch screech, like the brakes, at WOT, which ended up being the muffler tips.
Your sound might not be from intake, the horn it is only about 1/3 the opening of the air intake ducting.
Ignore other stuff in photo [that was to pressurize exhaust] once I had isolated sound with recording equipment. Also, plenums don't open when car is not moving, so you may need to be in motion.

Also "(during each gear shift)" could mean throw out bearing. Does sound change if you push on clutch at idle? That is near drivers side air dam.

 

[FF Drifter]

Any way you can post video of the noise? Even a basic cell phone video clip could help.

 

[silver2002]

The sound is posted here as a youtube


http://www.nsxprime.com/forum/showt...celeration-resolved?highlight=whistle+exhaust

youtube

 

[ntenseone]

I was going to suggest intake honk (Usually the reason for all the extra baffles and whatnot from the factory to eliminate such noises) but that sound is most definitely NOT intake honk!

I personally have to agree with Shawn. Somethung is up.

 

[jwmelvin]

But that's silver2002's sound, not the OP's sound. OP, does yours sound like that? I agree, the sound in that video is not normal.

 

[PghMiller]

Mine sounds very much like that, but not exactly. And I read his whole description of his noise, and everything he's saying is similar to mine... except the fact that he heard his more during the higher gears and at WOT (I hear mine the most during 1st, 2nd, 3rd, around the 2000-4000 rpm range).

In his video the first 2 sound clips sound the most similar to mine... the 3rd not so much. I will charge up my go pro and do some driving today.

I think my biggest clue is: why did the changing of the air filter from stock to UniFilter magnify this sound SO much??

 

[bngl3rt]

I think my biggest clue is: why did the changing of the air filter from stock to UniFilter magnify this sound SO much??

Exact same situation here. I never even noticed it before I put in the Uni Filter.

 

[shawn110975]

why don't we just put the OEM filter and box back in LOL kidding I still think it could be a vacuum sucking in air at certain RPMs

like if you blow on a piece of paper and can get it to whistle ya know.

 

[PghMiller]

I'm surprised that so many people have this screeching issue, but we (as the nsx community) don't know what it is. I will post my vids as soon as possible.

My thoughts are, being that the sound was present before the UniFilter but is now much louder with the Unifilter, then I'm assuming it has to do with the airflow. The UniFilter increases the amount of air flow allowed to pass through the duct and filter and into the throttle body, right?

Now that I look at the stock air intake resonator, compared to the downforce fiberglass/plastic one, couldn't this stock steal piece be the culprit? I'm placing an order for this DF one from SOS today and we'll see if that changes anything.

 

[G III]

i would disconect the air intake,,it sounds like a whistle,like a kazoo or somthing,,or like when you crack your window just enough and go the right speed ,,you will hear a whistle noise,,the uni filter increased the flow,,,,now it whistles louder,,,maybe a small crack in the air scoop ,or gap and it resonates or whistles at the correct air speed

 

[PghMiller]

But the noise is ONLY when I'm pressing the gas pedal. I could be cruising at 40mph with no noise, but the second I touch the gas pedal it will start screeching... and once I let off the gas it will stop.
It's funny, I could gently pump the gas pedal and it will: screech - not screech - screech - not screech - etc... with the pressing/not pressing of the gas pedal.

 

[G III]

you hit the gas ,the engine moves a little,,that small movement may make a crack or gap just right for whistle,,disconnect air intake from throttle body so air wil come from inside engine bay and give it a shot

 

[shawn110975]

what about the goose neck that the unifilter is connected to the intake is that new

 

[PghMiller]

what about the goose neck that the unifilter is connected to the intake is that new

I'm not sure what piece you are talking about. The black flex tube about 4 inches in diameter that connected the air box and throttle body?
Or the "resonator" that is inside the quarter panel that directs the air from the outside to the air box? (like in the pic posted above?)

Either way, my whole car is oem, except for the V1 exhaust.

 

[Mac Attack]

Hey, I just moved near Pittsburgh in the Cranberry Township area a few months ago.

I've had my '92 NSX for a good 10 years - mostly OEM so I'm familiar with the various noises they make (alternator bearings, A/C idler pulley, injector tick, valvetrain noise, OEM intake hiss with and without the Unifilter, etc). Sent you a PM with my contact info if you'd like me to take a listen.

Dave