I have been using a 1001 rb for a couple years now as my main stage rig. I also have a 400rb kickback combo that I keep at rehearsal. Here's my trouble, Ive recently added a Bass big muff to my set up and its dialed with tons of gain, trying to emulate the Muse tones. Im plugging my bass into the pedal then into the front of the amp. At practice, the 400rb loves the big muff, it handles the extreme gain no problem. However the 1001 rb hates it, i get instant feedback even with the instrument turned down. I guess you could almost call it a low frequency oscillation. In order to get rid of the noise, i have to reduce the amount of distortion, there-by losing the tone i desire. Any idea why one amp is different than the other?