had engine gasket replaced.works fine no leeks .

had it at gm shop.All belts and pullies are OK.They said it is definitely vacuum,but is not a gasket.they did not have enough time to diagnose completely,but mechanic thought it may be a sensor.if it is a sensor can anyone tell me where it is located. Thanks

IT DOES SOUND LIKE YO SAID BUT ONLY FOR ABOUT 39 SECONDS, IF IT IS THE AIR PUMP WOULD IT DO THAT ?WHAT S DOES THE AIR PUMP DO THANKS FOR YOUR HELP

I have had the air pump make that noise on several vehicles. The air pump supplies filtered air through the secondary air injection system into the exhaust system. This helps reduce emissions. So it's really only on during a cold start. It's located lower left of the engine. Easily accessible from underneath once the lower air deflector is removed or left front fender liner is removed.