sharp exhaust buzz with throttle blip

This seems to be an odd noise problem - I've checked the obvious, heat shields, exhaust system bolts, etc.

At idle I can quickly press the throttle, high revving the engine briefly, and get a raucous sharp buzz from roughly the catalytic convertor area. High revving at idle doesn't do it, although I can hear a slight "note" of it. It's hard to pin-point because it's loud and seems to come from everywhere.

Driving around at low RPM's and suddenly accelerating produces the same thing. Hard acceleration at higher RPM's doesn't.

It almost sounds "internal", but a recent engine replacement (pushing 140K miles I had a cracked head previously diagnosed on this forum!) hasn't changed this condition which has been around for 20K miles or so.

It's driving me and the neighbors and the toll booth operators crazy.

Any ideas???? Exhaust header crack maybe??

Which Engine Do You Have

Sorry - I have a 98 3.2L badged as a Passport. Original exhaust still intact (or so it appears).

sorry I am just getting back the most common thing I have seen with this type of noise on th 3.2l model is the muffler

Thanks for your reply. I believe you're correct after looking closely.

It doesn't sound like a "bad muffler" in the bombed out internals kind of way, but there's extensive carbon around part of the front plate seam to the body. I don't have anyone who can "blip" the throttle for me at the moment... but I believe a leak there would explain it.

I appreciate your suggestion. I'll double check and replace.