Hi clarkskull i have a RX 480 Red Devil oc 8gb and a similar problem, mine in idle is constantly at 1330 mhz and gpu usage fluctuating from 0 to 100% with temps over 60 degrees. This happens since 3 days, i tried all ( virus scan, malware scan, uninstalled drivers with ddu, switch on another slot pciex of motherboard, i also switched on the second bios of the card ) but the issue is always on. If i restart pc is fine but after few minutes without doing nothing the issue come back, if i play something the issue come out immediately. I bought the card on Amazon 2 months ago and tomorrow i will do rma. I don't know if this is an hardware or software issue. Please i need to know the cause of issue.
UPDATE i found the cause of the problem, simply is "windows defender user interface" that start hiddenblokingthe cardalso tried to put an old gtx 660 nvidia and the same problem. now i have to search how to prevent the program from auto start
"Idle" really isn't idle, your GPU is still under 2D stress from UI rendering, which causes the clocks to fluctuate.