SID with noise in C128 in mode

[Naquaada]

Hi!

I've got a flat C128 with a 6581R4 and it has a terrible noise in the C128 mode. If I switch in C64 with GO64 it is still present, but after pressing RUN/STOP-RESTORE it is gone. If I activate the C64 by holding the commodore key it is gone from the beginning. By the way, if I've got JiffyDOS activated this function isn't working, only when using the normal DOS. Crazy machine...

Ever heard about a noise in C128 mode only? There should be a way by soldering a diode between GND and ExtIn, but I bent the ExtIn pin of the SID away from the socket, the noise is still there.