when the rear window is up on my 89 4runner, the rear window mechanism inside the tailgate makes an awful racket. any suggestions to help surpress the rattling noise inside the truck. i'm not looking for the "crank up your stereo" answer either. thanks

 

Take the inside cover off the gate and remove the regulator assembly. VERY easy.
Check the rubber channels the window rides in for rot. If they look good, clean them real good with a rag & some light solvent or rubber-safe degreaser. Let dry, spray liberally with a GOOD quality silicone spray. Let dry, and spray a couple more times.
Clean ALL rubber/window contact surfaces the same way. This means the two weather strips on the top of the gate, inside and out. Also the channels on the truck itself.
One thing you may want to check as long as the regulator is out-the motor. Hook a 12 volt source up to it. One pin on pos, the other pin on neg. One way makes it go up, the other down. When I did this on my bench, I could tell the motor was giving out and the regulator was binding from corrosion. Corrosion was most likely making the motor work harder, which resulted in its' demise. These aren't real high torque motors.
Then make sure your regulator has no rust that makes it bind up. If you feel any binding, use a wire wheel on a drill to remove. Grease the assembly well and replace.
also do a search for this. pretty common. look at this one too: https://www.yotatech.com/forums/f116/more-rear-window-problems-105156/
I have a .pdf file of the fsm somewhere that shows disassembly lube etc. But it's pretty straightforward once you get it apart.
Good luck!
Jason