Rega P2- Power off Thump

The electromagnetic pulse from the motor circuit travels through the air etc and is affecting the coils in the cartridge and so the pulse is being amplified by the system.
It is a common occurence in some turntable brands, and not a "big" problem. If it was not happening before, perhaps your cable from the TT is too close to the motor or A/C wire?
On my 20 year old Rega3 it happens about 1/3 of the time, as I turn off the platter motor to change sides.
It is really not a problem if it is not too loud.

Thanks for the information Elizabeth. Now that I think back, this problem started after I replaced the Rega MM cart. with Denon DL-160 MC. So, does the EM pulse affect MC's more than MMs? BTW, the thump is not loud, just a little annoying thats all :-)

I do not know if it can be MM VS MC.. it is more a matter of individual cart design. And how the motor is shielded from the cart (In Rega no much!)