Chain Stretch.
 

I was riding this am and noticed even in a midrange gear my chain was making noise against the guard on a bumpy trail.

When I got home I checked and noticed that it the highest gear the chain is just really sloppy and I ordered a new freewheel with an 11 tooth 7th vs 14 so it would really get loose. Even in first it’s either a little long or just a really weak tensioner spring on the rear derailleur.

Have to admit I’m a little surprised by this as the bike doesn’t have that many miles.

Im going to dig up my chain breaker and take a link or two out. Any one else see this is a newish bike?

Sounds like the chain is little long to me. Even under the worst conditions, the chain isn't going to stretch that much

It doesn't take much rough ground to make a chain slap against a chainguard that is fairly close to the chain.

My old 7-speed derailleur cruiser would have plenty of chain to guard slap over rough ground.

My current single speed can have chain slap against the chain guard while going over rough ground as well. I like to cut through grass/dirt fields quite a bit and there is always a bit of slap. Not as much chain slap as the 7-speed though.

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 .