There are two tensioner bearings, one for the AC belt, and one for the alternator, PS, & waterpump. You can test the bearing on the AC clutch by removing the belt, give the pulley a spin and check for roughness and play in bearing. My tensioners w/120k make noise also.
I know this violates conventional wisdom but I've only had good success using WD40 in balky ignition locks. WD40 is a poor lubricant but its a great solvent and does an outstanding job of removing old lubricants and anything else the previous owner may have put in the lock. If you go this route, use it sparingly, and you've been warned.
I've had similar intermittent noises in my '93 525iM w/Marelli starter. This slowly deteriorated into an intermittent no start. I discovered a loose 12/13 mm nut on the solenoid, the nut closest to the starter. This connection carries all the current the starter draws so it need to be clean and tight. There was evidence of arcing on the washer under the nut. Unfortunately I didn't find it until I removed intake, in order to remove the starter and began to disassemble starter. You can reach this connection without removing starter, but disconnect your battery first. The other 12/13mm nut is connected to battery and is hot all the time.
Paul Shovestul
.....Got to keep the loonies on the paath.