Sounds like Belt tensioners and idler bushing talking. Try this trick, pop out the dust covers and spritz the mounting bolt (the center of the pulley) with any general lubricant (WD-40 for example) and see if you belt drive noise stops ASAP. At times its just the pulley being dry. There are just bushings in there. NO bearing per say.
You can use a stethoscope to determine which one is your noise maker.

Alternatives:
Main drive belt itself walking on start up. Check for chaffing on edges.
Less likely:
Alternator bearings.
Water pump

__________________

2005 X5 4.8IS
The Blue ones are always FASTER....

Current Garage:
2005 X5 4.8is
2002 M5 TiSilver
2003 525iT
1998 528i
Former Garage Stable Highlights
2004 325XiT Sport
1973 De Tomaso Pantera, L Model
1970 Dodge Challenger T/A 4 sp Alpine White
1970 Dodge Challenger T/A 4 sp GoManGo Green
1971 Dart Sport, “Dart Light” package
1969 Road Runner 383
1968 Ply Barracuda 340S FB Sea-foam Green