Rear Rear Bulk head noise

[nsx_2k]

Over the course of the past two years, there has been a progressive rattling (metallic or hard plastic sound) that has emanated from the right rear bulk head (behind the passenger seat). The noise occurs ~20MPH and/or when the is below 2500RPM. For reference, car is a stock 1991 NSX with no suspension modifications.

A prior search here on NSXprime yielded results suggesting that the front & rear panels of the ECU were rattling against the case. Per the recommendation, I wrapped the unit with tape to prevent the rattling. That worked great for two months and then the ghastly noise returned. This time, I used Plasti-Dip to coat the edges of the front & back plates as well as portions of the ECU's frame to prevent rattling. This was a heaven sent for the car returned to its glorious self with nothing but beautiful engine noise emanating from behind me. For some strange reason, two weeks later the rattling noise returned with a vengence.

In a fit of frustration (and anger), I removed both front & rear plates and disassembled much of the rear bulk head. The noise persists!!! For the life of me I cannot find its source. If I use a scope it appears to come from the ECU, but now I wonder if it resonanting through the ECU.

I suppose I should also clarify, this noise is fairly prominent and overpowers the sound of the engine. Sure, I could have the radio blaring, but that isn't the point of driving a NSX.

Anyone have any thoughts or suggestions on where to look? Or what to look for. I've attached a photo of my disassembled right rear bulkhead for reference.

 

[Thunder]

For my peace, I padded the back wall with polyurethane acoustic foam cut to the exact places forms a cover (acoustic foam for auditorium), it also reduces slightly the noise of the engine, in your case, it is possible that the noise does not come from the back wall and one element in the engine bay or under the car is loose (power cables, control cables to the gearbox and handbrake cables, brackets , fuel filter, pump etc. ...) lift the car and check all the elements in hand, sound travels faster through the aluminum sheet and the source of noise is hard to find
Last year, I checked the fasteners in the engine bay and I noticed that the rear window was not fixed, only 2 nuts were still tight on the left side, right nuts were loosened, just little to cause a noise disturbance: Smile:

 

[nsx_2k]

Thunder,

Thank you for the tip. I just looked in the engine bay. I recently had the fuel pump and fuel filter replaced. When I examined the fuel lines, I gently shook the fuel filter and a similar noise that I was hearing within the cabin can be heard in the engine bay. It seems that the source maybe the small holder securing the fuel lines to the body. I noticed the holder is loose, but can't tell how the lower "blade"-like component is to be secured. I'm curious if anyone knows how to secure the lower margin of the holder. It looks like it is supposed to wedge in between something. I've attached a photo of the holder in question.

 

[Thunder]

This piece is normally part of supporting the pipes (may be because it is difficult to see), it attaches (snaps) on the lower part of the opening of the firewall, yours may be broken and pipes vibrated against the aluminum plate, I'll take a picture for more precisely
ch...I'm sorry, my camera is too big and I can not seem to get a picture of this part :-(

 

[nsx_2k]

Just a quick update: I attempted to address the fuel line holder. I moved it around a bit so that it wouldn't rattle. Unfortunately, the sound continues within the cabin. During a recent drive, I got so annoyed that I pulled over into a parking lot & disassembled the rear bulk head. The parking lot I was in was quite bumpy & irregular. As I drove around the lot, the noise persisted; however, as I pulled more components from the rear overlying the ECU, the noise decreased. So it does indeed seem the noise is emanating from the ECU, but I cannot figure out how to abate the annoying, pestilent noise.

 

[Thunder]

The best way to find your noise is driving with the rear panel removed, take a passenger who can control his ears with his hands and noisy components, with a passenger, you can drive on different road surfaces, I wish you good luck for the rest, do an update when the problem will be solved: Smile:

 

[nsx_2k]

Problem solved!!! WooHooo!!!

Thunder, thank you so much for offering some insight that ultimately helped me resolve such a painfully annoying problem!

It turned out that the noise was actually coming from the passenger side engine cover (not glass) hinge. When I tapped on the engine cover, it was generating the annoying rattling sound within the cabin. The ECU cover did make a very slight noise originally, but I got that fully abated with the tape. After placing a torn portion of an old towel in the hinge for testing...the noise was completely GONE!!! I took the car for a drive on a local bumpy road that was dreadfully annoying before and now it is perfectly fine.