Exhaust noise/resonance

[Doc308]

Today I took my '92 out for its maiden voyage of the season and , man , it felt great ! However, toward the end of my 100 mile drive, I noticed that my exhaust note became loud/deeper upon deceleration--especially at higher rpm ranges.When this would happen, I could actually feel a resonation/vibration through the cabin. The exhaust sounds normal at idle and acceleration, but this occurs every time I let up on the gas. The resonance is very pronunced when this happens and is moreso when decelerating from higher rpms . I think I notice some very slight change in exhaust note when revving the engine, but it not that noticeable and nowhere near as pronounced when decelerating. Performance seems fine and there is no cel.

I took a quick peek at the exhaust when I got home and, based upon a cursory look, didn't see anything unusual--like roken hangers, loose shieds, holes, etc. In fact the exhaust system looks pretty good. The car has 79k miles on it and the exhaust is original oem.

Any ideas on this one--blown manifold gasket, rotting out cat/muffler/anything else???

 

[Doc308]

I took the car out for a test ride today and now I'm questioning if the noise is the exhaust at all. It feels like something rubbing against something at higher rpm deceleration . As I mentioned , it rather lod and resonates through the cockpit, with vibration through the floor. I'm now wondering if I have abroken/worn out motor motor mount .

As anyone had this happen? How difficult is it to replace motor mounts, if this is the problem. Help!

 

[LJSB]

Stop by the shop with the car and we'll find out what it is. I've been wanting to meet you in person anyway. :smile:

 

[Doc308]

Thank you, Vince! I'll give you a ring tomorrow.

 

[Doc308]

Joe--sorry I referred to you as Vince ! Also--I'm going to try to get to your place next week. Once agin, thanks for the offer to look at my car.

Anyway--there is anew twist to my story. I took the car to a good, local mechanic today ( although he's not familiar with NSX's) just to have a test drive/look/see on a rack. He could find nothing obvious and he thought that the motor mounts were tight. HOWEVER, after driving the car off of the ramp, my clutch pedal stuck to the floor and the gear shifter was stuck! We checked the clutch fluid and it was topped off. This remedied itself in about a minute.( Note that I had both the clutch master and slave cylinders replaced about 12k miles ago ).

Question--could the buzzing/resonance/vibration I'm getting on decerlation be related to the clutch? Also, if a motor mount is bad, could it cause enough movement so as to interfere with clutch action/shifting?