Better do a search on VANOS. I believe that car has it, and the system does fail. I would check it out before buying not just assume it is harmless valve noise.
It should NOT make noise. Do you think it did when new? Not a chance. My notoriously noisy M30 runs like a sewing machine, a German one. The M50 should be quieter yet.
Automatic trans? Better watch that with high miles too. These cars can be money pits in a big hurry. All you need is a cool head, a good inspection and test drive. If you are not comfortable with this, then maybe the BMW is going to blow your budget?
Current ride... '13 GTI Wolfsburg
BMW's from my past...
'92 535i/5 '89 325ix/5
'98 750iL '86 325(e)/5
'95 740iL '84 318i/5