by all means, please try to reinstall, restore, and update all drivers
, esp video. I'd even check the MOBO site for updates, and possibly flash the BIOS, if an update is potentially related by mfgrs description anyway. But I truely think its hardware issue.
if its a grfx card, try the onboard, to rule out a gfx card problem directly.
Since you recently built or changed part around at least, Pull every thing and reseat the contacts, visually double checking a proper contact between each part, esp the graphics card and even the cords. Believe me it can and has caused weirder issues. (and yes i understand the tests were fine, that does not mean the memory is fine, just that it can pass the stress tests given - a broken dimm can many times pass most any mem tester)
recheck every last BIOs setting (shadowing, GPU settings, shared/dedicated mem etc...)
finally rule out a conflict beween the parts first by researching the mfgr's website and finally by removing all nonessentials, one-by-one, until it works fine, then try replacing the last pulled item.
(prior case: graphics occassionally fluttered and static followed mouse, the problem, honest to god ws that the single HDD (which had no issues running windows and apps) was plugged in with an older unkeyed ide cord upsidedown...flipped it and it worked fine from that time forward...just making the point that logic can be tricky to intrupret when you have a pc made up of systems, each of smaller subsystems, and so forth.)