PML,
Let's just say we got off on the wrong paw, claw, I mean foot. Anyway, now we at least know what model ML you have. Were your Sources purchased new, how long ago and from an authorized Martin Logan dealer. You might see why this is important information later.
There are many people here with tremendous knowledge and many years of experience with Martin Logan speakers, but you need to give us quite a bit of information, because as I said before it could be something very simple or it might be something very complex, the more info we have the better recommendation that we can give you in return.
You might want to tell us how long it has been doing this. For example has it always done this since new?
Does it do it when you don't touch them?
Is your electrical system properly grounded with no ground loops?
What is your basic setup?
Does it do it on all sources?
There are many things I could ask and others probably will, but these types of questions will give us at least a basic starting point.
Oh and you might try calling Martin Logan customer service, they may have the answer on the tip of their foot, claw, beak, tongue.