Baffling Noise/Hum Issue with Certain Plugins (Melodyne Region FX, Slate Digital VTM)

Is there a good reason to use two soundcards? The most recommended driver, ASIO, only supports one card at a time (ASIO4ALL is not ASIO). However, the hum most likely roots back, one way or another, to using two cards, so unless you have a good reason to do so, use only one.
Also using more than one card often causes MIDI clocking and other timing/latency issues. All cards usually work best with their own, native ASIO-drivers. For some WDM works equally well.
 
Secondly, your post doesn't clearly tell how you're using Melodyne, but the rule of thumb and more or less a concensus on the forum is:
Open Melodyne - do the edits - bounce to tracks - remove Melodyne. Do not leave Melodyne in the active project.

Depending on how you read the post, the OP could be saying it happens when he uses his Xonar card and also when he uses his Alesis. I didn't see any mention of ASIO4ALL.

Perhaps he's using two cards and ASIO4ALL but let's not jump to conclusions here.

Hey guys, thanks for the responses.  To clarify, Sanderxpander is correct - I mentioned multiple cards purely for testing purposes.  I am only using one at a time, and I'm not using ASIO4ALL.  I'm using ASIO with all devices but with the manufacturer's drivers.
 
I've also found that this problem isn't isolated to Melodyne - it happens with particular plugins.  I've discovered that Slate Digital Virtual Tape Machines is also affected by the problem, which kinda sucks because it sits on the master track and has children on all tracks.  I can always bounce the Melodyne Region FXs to clips (as suggested, and I generally do, but I'm trying to troubleshoot this thing), but the VTM is a more annoying and permanent problem.

So it seems like certain plugins are causing some kind of feedback.  I can't find any literature on this anywhere, and even figuring out the correct search terms for something like this is difficult.  Going to update the thread title and original post with new information, and clear up the confusion with sound card(s).
 
EDIT: additional info - if I switch the RME Babyface from ASIO over to WDM, the problem persists.  So it's not a driver mode issue.   Also, I've just discovered that the issue DOES occur with my FireStudio Project, but it's way less prevalent - to the point where it's hardly noticeable unless you know what to listen for.  But it's actually good to know that it's happening across all devices, in a twisted way...