High Pitch Whistle, Screech under acceleration resolved

I had a nasty sound that I could not identify. I searched Prime for an answer and asked around. I finally figured it out and thought my six month odyssey might save someone the time it took me.

The Sound:


The mystery sound was barely audible from cabin, except when going through an underpass at full throttle. Several drivers mentioned it at Lime Rock and I was unofficially flagged at Watkins Glen for the noise -but we could not replicate sound in paddock by revving the engine; I was cleared to go back out. The sound did not occur unless the car was at speed.


The Details:

• Car: 2002 NSX; stock except for suspension mods., 48k miles
• Sound: Squeal, high pitch screech, whistle - like the sound of bad disc brakes coming to a stop.
• Engine [and all systems] ran great.
• Where: From rear
• When: Only under full acceleration above 5,000 rpm , barely audible in second, much louder in third; not typically in fourth above 5,000 rpm.

Steps:


At first I thought the noise was from the air intake or a vacuum leak, so I removed intake resonator [ inside rear divers quarter panel]- checked seal on stock air box, did a short run with stock filter removed , checked bellows, all vacuum lines and looked for obstructions in side intakes. Nothing.


Then, I thought it might be a bearing on A/C or Alternator [or worse], so I gently applied force to the pulleys to look for wiggle and went old school and sprayed the belts with a light soap and water solution. The sound was still there.


Next I used a digital recorder with a musicians microphone [ see photo- mic has clip and 7 foot cord] and recorded runs with mic at 4 quadrants of engine compartment: 1) between air box and fuse box 2) near hatch lock 3) right above alternator 4) below fuel pump resistor near AC - I was sure I'd find the source; nothing.


On a whim I put the mic in the trunk in the air pressure exchange opening [passenger rear]- and I heard it . Next I put the mic on the rear licence plate and heard it again.


Here is the sound - three times - first from cabin, then trunk, then plate -all in third gear.

http://www.youtube.com/watch?v=96tC6woCBFc


My next thought was an exhaust leak [ but remember, the sound was not reproducible at a stand still, only on the highway].


I made the rig in photo - air hose components and washing machine water line. I jammed that in one side of exhaust and made wad of cloth and closed off the other pipe. I applied a small amount of pressure [ stone cold engine ] and felt around the cats and around all parts of exhaust - I even used an incense stick looking for any disturbance in smoke around the engine and headers.


Then I noticed that, all though jammed up, both stock exhaust "tips" were blowing air backwards towards the front of the car.


I removed the tips [bolts sheared off] and the sound was finally gone. In cleaning, re-tapping welded nuts and putting tips back on I realized that they should have been about a half inch further on all the time - how they got that way, I don't know- they were misaligned slightly allowing pressure to build in the tip and blow back through connection point and tiny water weep hole at the bottom of the tips, possibly a perfect hole for a whistle sound [ on the photos you can see the heat discoloration on the engine side of the tips]. --- all's well that ends well. This good news simply means I have more money for Winter mods.

Wow! I believe I have the same whistle! My PO said the whistle was from the SOS Over-bored Throttle Body (but I'm not sure) because it is apparently much louder outside the car than in. It was apparently very loud at the track (NSXPO) last year. Often, I can't hear it in the car. Are you saying that the solution is to move the exhaust tips further forward? How do I know what is the right position without going through all you did to diagnose the problem? Amazing sleuthing on your part!

Thanks,
Gary

I have a crazy loud sucking whistle and love it

It's my intake and throttle body combination. I have to catch the throttle right and it whistles, sounds like a boosted kind of noise.

Gary:
The stock tips almost click into place, they go on and then can't go any further and create a tight seal at the end of the pipe with the tip. Mine did not create that seal, with force I could move the tip up and down a little. When it's on all the way, the tip surrounds the pipe on both sides. I had never seen them on all the way so did not suspect anything was wrong. Yes move them toward the front of the car if there is any gap.

silver2002 said:

Gary:
The stock tips almost click into place, they go on and then can't go any further and create a tight seal at the end of the pipe with the tip. Mine did not create that seal, with force I could move the tip up and down a little. When it's on all the way, the tip surrounds the pipe on both sides. I had never seen them on all the way so did not suspect anything was wrong. Yes move them toward the front of the car if there is any gap.

Click to expand...

Great! Thank you very much. :smile: I will give it a try. Unfortunately, my car is off the road for the winter, but I will take a look at the tips anyway. I won't be able to test the whistle until she goes back on the road in the spring.

Gary

- - - Updated - - -

I went out to look at my exhaust, and it is an Ark DTS which has the tips continuously welded with no gaps. So apparently, that is not the problem. Well, it was worth a look. <sigh> Thanks for posting.

Gary