https://www.acycles.co.uk/media/cata...ge_2_33027.jpg
note how the derailleur is mounted to the bike... They get bent very easily on these folding bikes.
Have the der. checked for straightness to the frame.... a twisted/bent Der. mount will cause all sorts of chain/cassette noise.... changing chain width a few thousandths of an inch will not solve the issue.
once the derailleur is true to the frame, readjusting the cable will get things running correctly.
Avoid laying the bike down on the right side... ALWAYS lay it down on the left side... this will help you to not re-bend the derailleur mount. Crashes often bend the der. mounts, too....