Just a quick follow up note (even though the thread is old I was advised it would be best to post here)...
the mbamservice.exe memory detections during custom scan have all but stopped over the last couple of weeks.
I had broken the custom scan into two, one with and one without memory scanning. Naturally, all the detections then occured in the memory scans. But it has now been a full week, at least, without any detections whatsoever (on either machine), and maybe just a couple prior to that, going back two weeks.
Perhaps either avast or MBAM changed something, or maybe it is the implementation of v1.50. Whatever the case, I wanted people to see the follow up, even though it involves resurrecting an old thread.