I didn't use the option given by Stefan since I really don't want to end up with a toasted laptop ;-)
But I tried the following option:
options nvidia NVreg_SoftEDIDs=0 NVreg_Mobile=1
(with 1 for Dell following documentation)
And it seems to give some improvements - I still get now and then a flashing screen BUT it does not continue every 30secs...