[Vwdiesel] Possible Alt. issue on my A4 Jetta starting to rear its ugly8

[Travis Gottschalk]

I am thinking it is more likely your alt pulley. It is a clutched pulley that sometimes locks up and causes lots of vibration in the tensioner and other times it can fail and free spin. Even rarer it can explode. The pulley is around $45 and the tools are around $35 to change it. I have the tools if you want to barrow. Take the belt off, put a screw driver in the fan blades in the alt (internal fan) and then try to spin the pulley either way. Should move one way. If it goes both ways or neither way then it is bad. You can still drive it without it working, just can't have everything on and you need to charge the battery when parked. 
Travis.
P.S. The pulley is hard to get off, Some have even broken the alt shaft getting one off.