Failed tamper roller bearing... Need advice

[audi4me2]

I had been experiencing some rattling noise usually when its wet from underneath my car. It comes and goes with wet weather and I took it to Audi and they said it was a tampered roller bearing on the input shaft of the rear differential, which is about 830 to fix. Someone else told me that the Audi diagnostic test was wrong because it's usually not tempermental. Well it rained again yesterday and now the noise is back but its making the noise even when I don't accelerate, but when I am just coasting. Someone else said it could be because my back tires are completely balb, but I have no idea what's making the noise. Does anyone have an opinion and do you think Audi was right about the tampered roller bearing.

[Spinnetti]

[a4_girlie]