I just replaced the s/c in my R53 (and lots of other things), and after several miles of driving, I started to get a loud screaming sound under load that varied with the revs. I poked around with a hose in my ear and thought it might be coming from the intercooler boot on the driver's side. I can loosen the clamps on that boot significantly, and the sound stops. If I tight either clamp a little, it starts up again. I'm confused! I don't see any tears in the boot, or significant warpage, and I took the intercooler back out and re-installed it with extra care to make sure things line up, clamps are well seated, etc.What could be going on?

 

Make sure your intercooler boots are seated on the underneath side. Sometimes they don't quite go all the way over the air horn.

 

Found it. Tighten those nuts, kiddos. This is the driver's side intercooler horn connecting to the intake manifold. Hope this helps some future dumbo like me who turns their MINI into a musical instrument.