No One Can Figure This Out

[M3 Mitch]

I'm going to guess the alignment of the pullies is off, and the nimrods at Toyota didn't check that. Could be as simple as missing a spacer or some stack of spacers is in the wrong order.

Is there any reason to think the alternator is under an unusually large load? I had a Datsun 510 that had a higher resistance short that caused the alternator to run at near max current when the car was running, but when off the short was isolated by the ignition switch. Long shot but worth checking out.

[HarryWho?]

I had this problem on a S 10 Blazer in the eighties. The dealer replaced everything twice to no avail. Just for the heck of it I bought a cheap serpentine replacement belt at Pep Boys. Never made noise again. I noticed that the OEM belts seemed stiffer and were a "harder" compound. The cheap belt was softer and more pliable but had no problem lasting the additional 4 years I owned the vehicle.