You may end up needing to RMA the graphics card then.
You should also have the issue in other games and stressful graphic applications, again try FURMARK.
I haven't used MSI Afterburner, but looking at the web site it looks like it has a "Memory Frequency" as well as memory voltage.
I'd try this:
1) find quickest way to prove graphical issues (Furmark? Unigine Valley? Game?)
2) Open MSI Afterburner, set memory to 90% of what is shown (i.e. 2,250 if 2,500), then SAVE
3) test for graphical issues
4) if gone, raise the memory frequency to where the graphical problems start, then backoff at least 2% (there are VOLTAGE options too but I don't want to confuse things)
5) If problem NOT gone put memory back to default and experiment with...