I've got the 99 SS LS1, have had it for 6 years now, it just hit 97,000 miles and has never had any problems. Lately though I have noticed an almost constant hissing noise coming from the engine bay. I was wondering if anyone has an ideas what this could be? I also heard that the 98 and 99's oil pumps tend to go out and if there's any early signs before they go? thanks

 

sounds like a vacuum leak to me. or maybe a dirty air filter

 

I haven't heard of the oil pumps making noise when they go bad. dumb question, but are you running the defrost or ac when its making that noise?

 

First thought is vacuum leak. The throttle body gasket went out on my lt1 and it definitely made a hissing/whistling noise.

 

Is it running poorly or thowing any codes? If not, maybe your just focusing on it a little too much. I did that when I first got my LS1, thought for sure it had a lifter going bad; turned out it was just piston slap.

 

well i've had it for 6 years now and I started noticing it. It sounds like it's coming from the engine by the pulley system

 

one way to check and see if it is an intake or vacuum leak is take a spray can of starting fluid and spray around where the noise is coming from while the car is running. if the rpm's go up, it's a vacuum leak. As asked before, does it always make the noise, or does it have anything to do with the HVAC system.

 

With the engine stone cold, pull the belt and start her up. See if it's the belt or pulley system.

 

for what its worth, check the gasket around the air filter cover. They are a pain in **** when it comes to properly seal them. Specially when you have an after market lid, which may not be your case.