+1. If you're hearing a dull (and possibly loud / somewhat violent) knocking/thunking, you're likely looking at an alternator. Mine did that then seized up...had my alternator rebuilt for around $200 at the nearest alternator shop, threw on new belt in place of burned up belt, all was good.
Sent from my SCH-I605 using Bimmer App
White 2007 Alpina B7
Supercharger clutch/bearings (check DIY), sunroof seal, quarterto8's 6000K angel eyes, bumper side mounts
Black 2002 BMW E66 / 745Li (sold)
KW v3's, blue angel eyes, 8000K headlights & HID fogs, rebuilt alternator, sunroof seal, CCVs, NGK Laser Platinum plugs, sway bar bushings, battery, timing & valve cover gaskets, valve stem seals, guibo joint, mechatronic sealing sleeve, trans fluid, alternator bracket mounting gasket, sanded headlights...