black00c5

I just bought a 2000 c5 with 74k miles and just noticed when I put the headlights down it makes a loud grinding noise for about 5 seconds. What could this be?

When I hit the gas something is making a loud whine noise and stops when I don't touch the gas. It also goes away if I drive it fast. It's a manual car. Most noticeable if you barely touch the gas. What could this be

GCG

It seems you probably have a broken plastic gear in the headlights.

Get a kit like this one (pay attention because there are 2 different kits: one for "97 to early 2000" and another for "late 2000 to 2004") and follow these step-by-step directions. You'll save money and they will last forever

You might need these as well (the rubber bump stops).

There is a TSB, that calls for shimming the driver's side motor. The parts needed for this are included in the above mentioned kit.

SaberD

the whine is most likely coming from the differential in the rear. I would first suggest replacing the fluid, but there are slim chances that will work. A differential whine comes from an incorrectly set up ring and pinion where the wipe pattern isn't in the center of the tooth. This usually occurs from some sort of foreign body getting caught between the gears and deforming the differential case which requires a re-shim to get the gear mesh back to normal. However, the shimming needs to be done on a new set of gears. Since used gears have already worn in the wipe pattern, the surface hardness is too great to establish a new wipe pattern. The only way would be to get the gears set up with the exact wipe pattern they had originally, which is next to impossible because (a) you have no indication of what the original wipe pattern even looked like (b)there is a bit of a range for acceptable values, (c) the range of adjustment shims isn't fine enough to re-match a previously worn in gear mesh after the case is deformed, and (d) if it's whining, the face of the tooth is likely modified from the original mesh if driven like that for an extended period of time.

If you don't have excellent mechanical skills, I would suggest sending your differential off to RPM transmissions or RKT56. Very few shops know how to rebuild these things.