almost certain 99% the issue is your cartridge. I beleive it isn't so much the type of cartridge, but where you live. you may be near a comunications tower. the issue occurs with Mc for sure, I bought a MED Output Sumiko SHO (2.5 mv) from another member her in NY for the same reasons. Over here in CA, i use the SHO w.o problems....
you may want to pick up an old inexpensive MM or if you have an old cartridge laying around, try adding it to the system to see what happens
you may want to pick up an old inexpensive MM or if you have an old cartridge laying around, try adding it to the system to see what happens