Well... after a few days of quiet a new one appeared.
More of a meatallic sounding click that is worse when you have the rear wiper going and pretty much goes away if you wedge a sponge between the glass and the rear trim (until the sponge compresses).
Diagnosis today is that the rear hatch trim needs replacing... and is on back order. So I'll let you know how it goes.
The car is a great drive, but build quality does seem to have taken a tumble from the E46.
