ZED 10fx noise on FX loop

Hi the ZED 10FX works ok along as I do not use the FX

The FX work but… they also create noise

So without any input you get ( gain and Level on 50%) noise with the used FX

I thought it could be the Main FX Poti and I opened the unit only to find that the pot is sealed so I could not clean it

Any help would be great