You guys speak sense! The car is back with the supplying dealer to fix and I have told them my theory re: engine mounts. I suspect that if they can't find an actual cause, they will start with the engine mounts and hope that's it. At least I will be able to eliminate that from the list of suspects if it doesn't help.

I wish I still had the car here now to test the mounts by jacking up the engine slightly.

I will keep this thread and my other one updated with what happens.