Alternator Belt Fails For Second Time

[DaveR]

1991 Audi 100 2.3E -- The alternator belt has always been noisy. after one broke we replaced it with second-hand one, (country garage) that lasted 4 years, but was also noisy. that broke and was replaced by a new one (correct size, but not genuine audi part). That was quiet for a while, then became noisy, and broke after only 3 months. Any suggestions on a likely fault. It was not over-tight, and the grooves don't look damaged. Could a fault alternator be too hard to turn? and therefore strain the belt?

Thanks