Strange, this cannot be intended. I would suggest you report this to service@zidoo.tv to make the developers aware that the "How-To Clear Data and Cache" Instruction is not fully woking. Maybe this needs to be adressed in one future FW-Update...
Probably the data and cache have been cleared... but it's the noise on the right speaker that persists... TBH, I do not think this could be a problem related to data / cache. It is either an imbalance at output level, maybe caused by DSP / EQ (@mmuetst, out of curiosity, have you checkd?) or some fault at the final output stage.
...But @mmuetst had mentioned that he already follow this guidance but his data/cache was NOT fully cleared. Therefore my suggestion to notify this to team Zidoo. They should know if their instruction does not perform like intended.