have a same problem
CPU: intel core i7 4790k
MOBO: msi gaming 7
GPU: msi gaming X RX480 4g
Driver version: latest
same issue here, after a while it starts flickering and the cause is the downclocking of the card. its been doing this since a couple of months now and im amazed that this is not getting addressed by AMD.
the only solution so far is to use some software called clockblock which prevents the card from saving power! way to lose customers AMD, great job of not fixing such nasty problems.
i would imagine that most people return the card with these issues so they must by now have a ton of "good" cards back because of this issue.