My 1994 Acura Integra makes a buzzing noise exactly between 3000 and 3500 RPMS. It sounds kind of like the sound a circular saw would make cutting wood. It only happens when I am accelerating through that range. Also, sometimes after driving for a while, it doesn’t last as long and the noise stops around 3300 RPMS. I’ve checked the heat shield and it seems to be fine so I don’t think its that. Does anyone know what this could be caused by?
Probably still a heat shield. It is very common on that car. Our spare is a 95 integra and it had the same problem while not being obvious.
Look under the car towards the muffler. Tap on it with a rubber mallet - not too hard but see if it wants to rattle. Most likely one of the heat shields on the catalytic converter has one of its mounting ear rotted off.
Of so, go to home depot’s plumbing department and get a large band clamp. Wrap that around the offending shield and snug it up. That’ll stop it.
Remember that there are two heat shields. One below that’s easy to see, and one above. Even if they’re still securely attached with no broken welds, it’s not uncommon for a piece of gravel to get stuck in one and rattle, so it’s a good idea to bang on it with the palm of your hand (when cool, obviously) to see if you can get the rock to jump around and make noise.
My '94 Integra GSR had probably the same problem; buzzing noise at 3k RPM. Finally tracked it down to a small baffle that’s inside the exhaust pipe, where the two sides from the engine come together. After a while the welds break loose, and it buzzes back an forth with the exhaust flow. There’s apparently a service bulletin on it, which the mechanic finally found well after the warranty had expired. He said it was not dangerous, and we didn’t consider it worth fixing. The car has 250k mi on it now; I suppose it still buzzes, but I don’t really notice it anymore.