You sure it is the freehub usually crunching noise is crap in the chain as it connects the gear teeth. Degrease your chain, wipe it all off and get between the chain links. Then put a quality dry lube on it. You will have to clean the rear cassette and front chain rings as well as any mud left there will get back on the chain and problem starts again
Watch the video more closely. The crunching was occurring while the rear wheel was free wheeling, nothing to do with the chain or cassette, as it crunches the hub lightly engages while the wheel is spinning turning the chain.
The chain and cassette was squeaky clean when I took the video anyway. I use a park tool chain cleaning tool and degreaser after a wet ride.
The bike shop has fixed it for me, there was apparently a slight misalignment of the free hub body which with a little pressure caused the horrible noise and caused it to lightly engage while free wheeling.
Anyway they disassembled and serviced it for me and it’s running sweet now.