Alternator drive belt
 

MX3 Coupe - Automatic first registered 2003 1.6 4 cyl DOHC
2 new belts in 3 months, alternator & regulator checked out OK.
Pulleys in good condition.
Tension OK.
Any similar experiences out there, any possible reasons / solutions.

Same brand of belts?

Have a very close look at the pulleys & make sure they are all lined up 100%, no wobbles or vibrations & make sure there are no small stones or foreign objects jammed in the ribs of a pulley.

same as above - could well be a bearing gone in one of the pulleys which can cause the belt either to squeal or slap.

I had a similar problem on my Mazda 5 and the dealer wanted to change the whole tensioner for £150+ saying its was the tensioner spring when it was only the bearing that was gone. I got the pulley wheels off ebay for about £20 and changed it myself

I have also had problems with aftermarket belts on other cars being too long