Are you sure it's not the one way clutch pulley on your alternator causing the problem? I recently had a problem on my A4, changed 2 tensioners and still no better, turns out its the clutch pulley goosed on the alternator. Easy to check if it is

absolutely positive.
the alternator doesnt have a clutch, is on a different belt and on the other side of the engine.

you dont know the 300TDI lump, do you?
 

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