I have a 99 Civic starting yesterday the car makes a buzzing kind of noise at about 4K RPMs. The best way I can describe this noise is the noise that the fire work, I don't remember the name, you set on the ground and it spins and shoots sparks. This is the first thing I thought of when I heard this sound. The sound continues through execleration until the gear shifts and then we start over.

 

Can you hear it under the hood? sounds to me like maybe an alternator or a/c bearing possibly. Maybe power steering pump. Really, it could be anything that spins with the engine, hehe.

 

possibly catalytic converter heat shield?

 

Uh, sounds to me like an exhaust leak

 

i would have thought it was a loose pulley....

 

no, it's just the particular exhaust frequency hitting it's peak and reverberating in the exhaust. that is if it drops off in higher rpm. if it doesn't it could be something to look into.

if you havn't had any exhaust work done lately (cat back, swaping parts around from other chassis...so on) learn to live with it untill you get a chance for something new. if you can't stand it, have a different resonator put on. that may help.

if you decide that it doesn't go away after 4k or so, you can check for leaks by letting the car idle in a well ventilated area, plug the tail pipe with a rag and move around the car to listen for excessive noise from anywhere else in the exhaust. if you put it up on jack stands you can also feel for exhast leaks with your hands. you'll feel it blowing out if theres a hole.

 

I don't know how I feel about stuffing a rag in the tailpipe... but you should be able to find the leak by jacking it up and feeling around for leaks (carefull not to touch the exhaust with your forearms!). Check all the flanges, but really inspect your resonator, muffler, ... anything that hangs low in your exhaust system and might be scraping.