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:
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.
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.
