My Lux 7d Fat tire has a conventional type full chain guard and I’ve experienced chain slap or rattle , since day one .
IMO , derailleur bikes weren’t designed to have conventional chain guards. It’s happens because of the chain line angle of the rear cassette or freewheel.
My Specialized Roll has a chainring chain guard and the chain will “Ching “ when I shift into low granny gear . I’ve already removed the inside guard , thinking of removing the outside one too .
I only need a chain guard about four months out of the year , when I wear long pants. I can use a pant leg wrap during that time .