only sometimes when I turn it up. Like it gets stuck and if I tap it the hum stops. What would be the cause of this? It seems like a connection issue.
MARTY FRIEDMAN--"It’s a lot easier to be technical than it is stylized; it really is... But I think it’s a lot more rare to have someone who’s really got their own sound because that’s something you can’t practice."
The grounding wire is probably loose. Take it in, get it fixed, no big deal (or if you're decent a soldering do it yourself)