Turntable Hummmm


Suddenly, without anything being touched on my system, I have a hum coming out of the speakers when the stylus hits the vinyl. Its not real loud but it is there. I've disconnected everything and reconnected and it is still there. Any ideas how to find the culprit?
azmoon
What cartridge are you using? Does it only do it when the stylus is in contact with the record, or is the hum there when the stylus is over the record?
I am using a Rega P25 with an Exact 2 cart. The cart is 6 weeks old and has sounded great. The P25 does not have a ground.

The hum occurs only when the stylus is in contact with the LP.

What is a ground lift plug? Thanks for the input.