I've noticed that when I start my '99 LTZ, I hear a buzzing sound from underneath the car. I only notice it right after the car is started. I can't really tell if it goes away after driving a while or if I'm just ignoring it. Anyway, it seems to be coming from behind the rear tires. Is it the fuel pump? That's the only thing I can think of. Any clue?? Is this normal on this particular year/model?

Instead of inserting the ignition key and cranking it immediately, turn the switch to RUN and listen for the 2-second fuel pump prime cycle. If the sound is the same, that's the noise you hear while running. It can be completely normal. I've had relatively noisy fuel pumps go on for years making a similar buzzing noise.

No, I don't believe that's the case here. The fuel pump seems to make a quieter noise. This specific buzz is a little more high-pitched. The only way I know to describe it is to compare it to the "buzz" of an older pick-up truck, when the key is in the ignition and the door is open. It's not quite that loud, but it's the same basic noise. Like I said it is coming from behind the rear tires - I guess it could be normal...I still love her anyway!!!

your emissions canister is located near the trunk on the drivers side. What you are hearing is most likely the canister purge vent solenoid and nothing to worry about. Most older GM vehicles had the canister under the hood, so you'd never hear it over the engine running.