Accord Exhaust Noise

I have a 1994 Honda Accord with an automatic transmission. At 2800 rpms and up the exhaust makes an annoying groaning noise. The exhaust has no leaks. One mechanic referred to harmonic resnance. Any idea how to resolve?

Has there been any work done on the exhaust system? You say 2800 and up. Does that mean the annoying noise never goes away, regardless of the rpm?

A heat shield can rattle at a certain rpm, but it usually stops within a few hundred rpm.

Does this car have a non-stock exhaust system?

if the noise does stay after 2800 rpm, and NOT go away i would think you DO have an exhaust leak. it just shows up under high pressure.

if it does go away with a change in rpms, look at all the hangers. maybe one or two are rusted out. the harmonics (if any) would be from a vibration, but usually not at all rpms.

Thanks for the response.

My mechanic ruled out a heat shield issue. We removed the rusty, somewhat loose one under the hood just to be sure and it made no difference. I’ve had heat shield issues in 2 Civics and the noise was quite distinct and not like this current problem.

Once the noise starts it does not go away (I’ve run it up to about 3700 rpm and the noise remains, not sure if I run it higher)

Honda issued a service bulletin in 1996 that addresses two exhaust problems with 94-96 Accords - one at 1800 rpm and another at 2000. The bulletin suggests installing a “kit” which includes 2 gaskets and 4 spring bolts installed engine side of cat converter. We figured we’d try the kit so my mechanic installed it and there is no decrease in the noise at 2800 and up.

I bought the car used and do not have service records for exhaust. It does not appear to be original. I am aware that non Honda parts/cheap stuff may lead to exhaust noise.

Any idea how to figure out which part of exhaust may be causing the problem?

My response above to mcparadise addresses most of your comments/questions.

The hangers have been checked and one was rusted and so replaced. The others seem fine.