Well I just got my 95 z28 out of the shop. Needed work right after I bought it so it's been in there since the day I got it. Anyway I got it back tonight and was letting it sit and run at idle while talking to a friend and about 15 min into it I heard a short buzzing sound coming from the rear end near the gas tank. It continued to occur every 20 seconds or so repeatedly. It's like a one second buzz almost sounds like whe a phone on vibrate rings and buzzes on a table or something like that. It also did it while the car was off but the ignition was turned to on. Weird. What is it? I have a video if needed (although there is a stupid conversation also going in in the background). I can't find any other thread that has this particular problem. It just had the water pump done, a secondary air pump (?), and a radiator hose replaced. Any idea what this could be? Car seems to run well.

 

Fuel pump

 

Fuel pump doesn't continue to run "while the car was off but the ignition was turned to on". Only runs for two seconds if the engine doesn't start, so that's not a likely explanation.

Does your car possibly have a CD changer in the left rear fender cubby? Do you have a power antenna?

Hot fuel could also cause the fuel tank pressure relief valve to vent periodically. There is one pressure control valve that vents to the charcoal canister in the driver's rear fender, and another pressure/vacuum valve the vents to atmosphere right above the rear axle.

 

No antenna, no cd player. Should I be worried about it?

 

I'd try and track down the exact location of the noise, even if it requires crawling under the car.