OK....i have a 94 gsr with 37,850 miles on it....i just bought it used a month ago but the problem is that i hear maybe a vibration sound around 3500-5000 rpm...but i dont feel a vibration...im guessing its my exhaust but i dunno....but usually it doesnt make as much noise if i use my a/c......if someone knows wtf is wrong with my car please lemme know...thanx yall peace

 

Is it somewhat nasal? I had a rattling that started just before 3.5 and lasted untill about 5 and only happened after the car was warmed up. It was the infamous a pipe rattle. Apparently you can take your a pipe off and beat it with a large heavy object to fix this, seriously. What is going on is that the a pipe has a tube within a tube and the inside tube breaks free and rattles around, and by beating the outer tube it dents it thereby holding it against the inner tube. Another option for fixing this is to take it to a muffler shop and have them cut the a pipe open and reweld it (don't know any exact details on this). I also had a raspy sound that seemed to have come from the heat shield behind the stock manifold that happened at about 3.5 k especially when the engine was decelerating.

Another possobility is that it could be the heat shields around your catalytic converter, which is a problem that I also have. This is present from idle and randomly elsewhere in the rev range, and is a much quieter raspy sound that I notice mainly when parked next to something thereby magnifying the sounds coming from my engine. This can be cured by unbolting the heat shields. If you do this don't drive over flammable material as those heat shields do serve a purpose.

Hope some of this helps. BTW, I also drive a 94 GS-R, but with about 100,000 miles on it.