Unusual alternator belt problem

[Aidan]

Hi guys, Had my 940 tic for excactly a year now, and I have a strange problem with the alternator belt, the teeth keep breaking off the belt and it ends up shredding itself to bits, since I got the car I've put 6 new belts on it, so roughly every 2,500 miles. I've done all the usual, checked all the pulley's etc for damage, alignment etc, there all fine, used all different makes of belt (Volvo origional, Gates etc) tried running the belt loose, tight, in between,,, still keeps breaking them, any idea's, thanks.