99er

I have a 1999 tahoe and have a siren noise when the air pump turns on when first starting the truck up for about 20 seconds. I have replaced the air pump. Replacing the pump doesn't fix the problem as the siren noise eventually comes back within a few days. I had also replaced the check valves recently, and the smog pump again, but the siren type noise stops for a day or two, but eventually comes back after a few days. It lasts about 20 seconds and seems to be more pronounced when the engine is hot and has been running for a while.

There doesn't appear to be a relay for the air pump in this vehicle which is puzzling. Under the fuse box cover there is suppose to be a location for a relay marked (AIR) which I presume is for the air pump. However the relay is not present and the connection leads are not present either...so maybe this car does not have one?

I'm just puzzled and don't know why when the air injection pump comes on, there is that siren noise for 20 seconds. It's annoying and I'd like to fix it. Any ideas? When I removed the hoses to replace the old check valves there wasn't any water coming out. The noise only happens while the secondary air injection pump is running.

Would it be wise to replace the hoses perhaps that go from the air pump to the check valves?

I really am just not sure what else to do and am pretty tired of blindly throwing parts at it.

99er

Bump.