OB-6 stuck at boot - mirrored C and loud pop sounding

[Beevolver]

Some months ago quite recently after I bought my OB-6 I updated it's OS to 1.6.6.

Cant tell if it's due the new beta OS or not but if I reboot the synth after being powered off for some hours or days then it have startes getting stuck in a weird mirrored C error and sound a loud looped pop sound.
If then rebooting it again it works as normal.

Anyone else got this error and any solution to recommend?

Want my OB-6 to be healthy and feel as I really started loving it.

[Soundquest]

Never seen that or being stuck in any mode for that matter. 

[Beevolver]

thanks for the comment Soundquest.

A video tell more than 1000 words...

[Beevolver]

another video including the rhythmic stuck sound...

as long as the workaround is working and the problem doesn't get worse I can live with it but of course would like it resolved. this is my most loved and most expensive synth and would really like to assure it feels well.