I have a very intermittent problem where the instument cluster (or something behind it) will make a loud buzzing/vibration noise at right around 3K RPM. It's loud and sudden and scares the crap out of me when it happens. Each time I've quickly let up on the gas - RPMs drop under 3K - and it stops. It has happened about a half dozen times in two months of driving the car.
Any theories?
BTW... Its a '93 LE 4cyl which had an engine transplant just before I got it.

Don't know if it's totally electric or if it uses a cable but, if the speedo uses a cable as the speed input from the transmission it may need to be lubed. It's a metal rod inside a flexible steel sheath. I've got one on my 87 that needs to be lubbed now and then. Makes one hell of a warbling grindy noise especially when its cold out. I just use 3 in 1 oil. I'd like to use graphite but, I can't see a way to get it in there. Let us know what you find.