Vibrating sound at 1800 RPMs

[Culpeper]

My "new" 1990 V6 4Runner has a vibrating sound at approx. 1800 RPMs. It sounds similar to a loose dash vibration (a sort of low groaning vibrating sound). There is nothing adverse in the way the motor is running or the way the vehicle is handling during this noise. It has an automatic transmission. The noise occurrs with the overdrive switch turned off or on as well as the ECT power switch turned off or on. It sounds almost as if the tachometer itself is groaning at this RPM range. I was wondering if anyone might have any ideas? Other than this annoying noise everything seems to be running okay.

 

[Culpeper]

For further reference.

Resolved the noise I was describing;

Using chassis ears pinned down the noise to the left fender well. Insulated/tightened down air filter box, mount point from fender to radiator, alternator wiring harness. The noise was harmonic meaning at a certain rpm range under load it would create a vibration through the left fender well. The noise/vibration would travel this area of the chassis like a bell and reverberate behind the instrument cluster inside the cab. So much so that to the naked ear you could swear the problem was with the dash or instrument cluster area.

I appreciate nobody spamming this thread with standard BS like, "you sure there isn't an 18 wheeler going by when ya hear it!"