Because it is a 2006 model, the links below may help, i believe there was a problem with the bolt holding the sprocket that connected the crankshaft timing chain to the overhead cam chain working loose, it can cause major problems if it brakes, sorry for the bad news, but better have it checked out. Not sure if you can still have it fixed as good will from VW's, has I believe it to be a common problem on the 2006 Passats. Peter.
B6 Passat V6 timing chain failure
VWVortex.com - Timing Chain Replacement on 3.6L 07 Passat (65k miles)
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