CadeS7

While the engine is cold, my car has developed a fairly loud high-pitched whistling near the passenger side airbox for about a minute or so after starting, then there is a sort of deeper-toned winding down noise after which the noise disappears. I'm assuming it's the SAI pump. Is the pump below the passenger side airbox like I'm thinking? If so I'd say it's almost certainly the issue. Anybody know if it's fairly simple to replace?

dvs_dave

Yes and yes. There’s 2 of them down there.

MP4.2+6.0

Yep, twinned, so you need to figure out which one. And...from ask me how I know...be sure the drain hose for air box just above is not kinked. If it is and water backs up, air pumps probably draw their air from there if same as the also twinned box W12. Then clogged drain = pumps can eat water. When I pulled off the first hose from the pumps I knew which it was. IIRC you can spin each pump up with VCDS in a test mode. At time I powered them with a 12V lead fed in through fog light grill opening I had pulled off. My water logged one was completely dead.

Assuming you need to replace, either used as one option or maybe OES. Pricy from dealer. OES was Pierburg on mine, which Rock Auto had at time.

CadeS7

Confirmed the noise is from the passenger side pump. Might try and find a used one (or two) before spending what seems to be $600-$700 from Audi, because nowhere else that I can find has new ones. I'll definitely check out the drain hose too when I get there. Thanks for the help, I'll let you know how it goes.