My Mk4 is due to be swapped out next week due to a similar problem. I had real issues when the weather was warm/hot in that the Mk4 would not recognise the DVD & would actually keep rebooting. Taking the DVD out it was roasting hot, and I also wondered if the fan was U/S - I mean the boot area wasn't that warm. Mine is very unreliable now in reading a copy DVD...

Dealer did some diagnostics and agreed to swap out the unit.

So, all in all, I'm quite pleased as I have just had a new Climate module AND a new (& upgraded) BM54 tuner.