I received my headset and it was fine for a few seconds and then this erratic popping/crackling sound began (random intervals between the pops). It is like listening to an old record.
It does the same thing when I plug audio buds into the 3.5 jack.
My wife can hear the sound from the couch so it is pretty distinctive.
I've also tested on 2 computers with the same result.
Is this also in Home not in Games? If Games then I'd try reducing the offending settings. In Elite it was FX QUALITY...set it to LOW or OFF & VOLUMETRIC QUALITY set to LOW or Medium. It got better as they found the issue.
This is in home as well. In fact it even happens with the rift sitting on the desk and nothing "playing" at all (be it home or a game). But I can hear the occasional crackle/pop from the speakers. The best way to describe it is the effect with old unshielded appliances like washing machines and what they'd do to analogue radio receivers.
My audio is mostly fine and so far I have only found one title, theBlu, which suffers from distortion/clipping. I think perhaps the Rift S struggles with the low frequency sounds. I am running Win 1903 with the hotfix.