I have 1994 Honda Accord with an automatic transmission. At around 2800 rpms and up there is an annoying groan from the exhaust system at a steady or increasing throttle. There are no exhaust leaks. One mechanic called it a harmonic resonance problem. I found info. on Accord exhaust noises in the 1800 to 2400 rpm range but not for 2800 and up. Any ideas?
I’m going to agree with your mech.
Aftermarket mufflers and exhaust systems have proven to be a source of a resonance problem occurring at a number of rpms. Not just Hondas either.