Hi Eric
I never had this problem, so I am only guessing:
(1) Wrong orientation of front flex disc (warm -> rubber is softer?), usually
there is a label on the flex disc stating: "Diese Seite zur GLKW=This side towards drivetrain". If not, you can determine orientation by checking the rubber enforcement of the holes: they should be after the holes in reference to turning direction.
(2) shot transmission mount (warm -> softer rubber, more sagging?)
(3) less likely IMHO exhaust mounting bracket, from tranny to pipes
Good luck, Bruno