Rich, welcome to the forum. Have you tested your Rotex connected to a regular electrical outlet to see if it exhibits the same problem?
If you don't get the problem resolved, I would recommend that you contact Festool Ireland:
TTS Tooltechnic Systems Ireland Ltd.
E12 Calmount Park Ballymount
phone: 00353(0) 1 8642240
fax: 00353 (0)1 firstname.lastname@example.org://www.festool.ie