Channel II & III BUZZ!!!

[FattyMatty]

I just acquired a Crate GT1200H half stack.  I love the sound of all the channels.  However, when I switch from clean to the dirty channels I get a serious buzz/hum.  It seems to be directly related to the gain.  As I turn it up, the buzz/hum increases.

So what can I do to fix this? 

Can I just run my effects pedal through channel one to avoid 2 and 3?  The only problem with this is I have yet to find a sound on my Korg AX100 that I like better than the Crate.  So is there any other way?  Is it possible there is a fix for this, or is this just what comes along with a cheap amp?

Thanks guys.

[FattyMatty]

PS - I'm just looking for a starting point.  Maybe someone can suggest a couple places where I can start looking. 

I'm not being lazy - I did look through the buzz/hum sticky tutorials, but they are too technical for my understanding. 

[FattyMatty]

I just did hours of research and I keep hearing people recommending a ground loop isolator. 

But aren't these usually used when there are multiple amps and pedals involved?  I dont have ANY other equipment plugged in.  Just one amp with the gain cranked!!

[teemuk]

Does it buzz without the guitar?