GK MB500 post-EQ DI noise issue

[Gravy4001]

I'd really love to send a post-EQ signal to FOH but when I hit the button there's a significant buzzing, enough to require switching back to pre-EQ and then it's perfectly quiet. The ground lift button has no effect and it's happening the same in all different venues. I've searched on this and didn't find anything specific to the post-EQ signal. Anyone else ever experience this?

More info: signal runs from bass into a small pedal board (MXR compressor that is on all the time, EBS Octave off, MXR overdrive off, Boss chorus on usually), out from the chorus pedal into the GK head. I've tried turning the pedals off and it has no effect on the DI noise. Next outing I'm going to try bass straight into head and I also have a backup MB500 that I'll swap out and see how that one does.

 

[Downunderwonder]

Since it is quiet with all the other junk between bass and amp input, the noise comes from the GK preamp. They are usually very quiet so I venture it is faulty.

 

[Jamarvic]

Bringing this thread back.
I have this exact same issue too. This the second one now with problems. I bought it new over a year ago from sweetwater, it was a replacement because the 1st one I got was defective, it kept cutting out. I'm bummed out
I don't mistreat my gear and never had any problems with previous amps I've owned