Muzishare X7 - Pop in Right Speaker when turned off?

This happens with the volume all the way down, can have the selector switch in any position, pre or main amp 
switch in either position and only when the amp is set in ultra linear mode.

When in triode mode all dead quiet.

Amp has about 20 minutes on it from new, bias in spec.

I have no factory warranty on it but I may have the option to return to seller for refund..

Could this be a simple fix? Any ideas?

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I have the same amp and the same issue. From what I could find online it is normal for it to occur in ultralinear mode, the explanation was it is a capacitor discharging.

I usually use triode mode but when I don't I just switch it back before turning it off.

Very impressed with the sound and build quality of the X7. I upgraded the tubes and it's even better now.