I had the visual symptoms, although none of the relay clicking symptoms with my previous HD621. It eventually stopped passing an image through completely, although sound was never affected.

I ended up replacing the HD621. Didn't think about the power supply, annoyingly. I hope you have luck with that path.

Chris
Srces: Wiim Pro | OSMC Vero 4K+
Procs: HD621 > G61R > Minidsp DDRC-88D
Spkrs: 7200.2 + 5KC + 5Ks | iNuke6K > USC15 | iNuke3K > 2 x Crowson T108SS
Video: JVC HD950 & 1.9m React3 2.4:1 screen
Room: 5.8x2.8m | Various GIK Panels