If there is problem on HDMI but not via SCART, I don't thin this is a hard disk problem, I don't think is is a Custom firmware problem either. Humax have 'fiddled' with HDMI handshaking on almost every release, so if you don't have latest CF compatible version (1.02.32) I would try that. If you do have this version, all that is left is swapping HDMI cables (which you have already tried), using a diffearent HDMI input on your TV or maybe trying a different setting on the remove control >> V-Format button
The HDMI changes will be in the Official Humax software part of the code rather than the custom firmware but obviously the CF version number must match the Official version. The V-format button toggles different video resolutions e.g. 576, 720, 1080i and 1080p, the first 3 will result in a lower resolution picture but swapping between the two 1080's will only have very subtle differences, however they may carry out HDMI handshaking better, also 720 won't lose any resolution if your TV is only 1380X720 pixels, rather than 1920X1080
Perhaps you should start a new thread in the HD/HDR-FOX T2 Customised Firmware forum.Now i need to find a solution to my web-if connection problem - is it worth reloading the CF again?