Weird Sound At 3000

I have an 88 v6 4runner... My problem is whenever the tach reaches 3 grand it starts making this really annoying sound. It usually dies off at around 3400, but if you listen closely you can still vaguely hear it. It also seems like it goes away after ive been driving for a while (30+ minutes continuesly). Ive tried upgrading the quality of gasoline, and have also put some fuel system cleaner in and none of that helped. Any ideas would be great

It is probably just a harmonic vibration fundamental frequency of your engine. If it is, there is nothing, outside of balancing your engine, you can do for it.