97 Accord "Buzzing"

Hi,
I have an accord that made a "buzzing" noise at exactly 2,000 rpm's. It
sounded like it was coming from some part of the exhaust. I brought it to
a mechanic and they replaced the flex pipe.
The buzzing at 2,000 rpm's is still there but its quieter but now it does
it all the time between 2,000-3,000 rpms. Its worse now then it was when
it went into the shop!
PLEASE HELP THIS NOISE IS DRIVING ME NUTS!!

Also, on the highway when you step on the gas the rpms drop a little
without letting up off the gas. I recently changed the timing belt and
water pump at the same time as the new flex pipe, could that contribute to
the problem?

Any help is greatly appreciated.
Thank you

 

Check that the exhaust pipe is not touching some part of the car somewhere
along its run. Also check the heat shields around the catalytic converter &
muffler for looseness or distortion. These days, exhaust related buzzes and
rattles are caused by loose or damaged heat shields.

Unlikely, unless they messed up something else when they did it, or got the
timing off. Are you sure its not the lockup clutch engaging in the
automatic transmission when you reach cruising speed? It will drop a couple
hundred rpm when it locks up.