Hi Shawn
I recently purchased my Machinedrum UW and it had exactly the same problem as yours seems to. One output was significantly lower in output than the other and a bit crackly. I sent it back for repair/replacement.
Its just arrived back with me and it seems to be fine now!.. phew... After a few days though I thought i had another problem which was that one channel had slight crakle everytime a bass drum hit...or some other low frequency...yeek!!
I spent a day or so trying every combination of leads etc. and still the same problem. I then noticed that I couldnt hear the problem thru my monitor speakers but only headphones!!... so I took my headphones apart and found a small piece of grit which was rattling around when the lo frequencies hit... DOH!....
Hope yours gets sorted finally!