I hear a short flutter a half sec after the engine starts that may be tension from startup comming off the belt and the belt fluttering as the engine settles into idle.

You could test that if you are brave by using an 18-24" tight fitting bar and releasing the tensioner bolt and holding the tension of the belt with the bar after the engine is started. One MUST be carefull to have a good grip AND control of the lever one is holding. This is easier with a longer rather than shorter bar.

By slowly reducing tension while running I'll bet you can duplicate the noise you are hearing.

I've done this to test for vibration at the tensioner assembly. It is easier the second and third time you do it.

ps: all my tensioner woes were due to bad motor mounts. i burned up numerous tensioner components B4 discovering that. If yours are OE you might want to check the tops of them for cracks/separation.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)