Help me troubleshoot this mtb, please

I don’t get stumped often, but I’m stuck here.

2018 Giant Trance, Sram Eagle GX.

Under load, the chain “pops” on the cassette, as if it comes misaligned and then snaps back into place on the cog. Not quite as heavy as when the chain almost shifts to next cog, but definitely sounds and feels as if the chain is coming un-meshed from the teeth and then popping back into place. This happens in most of the cassette, so I don’t think it’s the “teeth tolerance” issue I’ve seen people discuss regarding a specific cog.

Bike pedals and shifts flawlessly in the workstand.

So far I have checked/confirmed:
New chain
Cassette does not appear worn
Hangar is straight
Torqued all suspension pivot bolts
Torqued rear through-axle

I’m stumped and it is keeping me from riding in beautiful weather because I can’t stand a noisy bike.

If it only happens under load it is most likely a worn cassette…how many miles on the previous chain and how many miles on the cassette?

Don’t know about the mileage, this bike doesn’t do too many miles. I replace when stretched. This cassette has seen 3 chains, I believe.

I’ve had similar things when the cogs got worn, I’d second that theory. It can be really hard to tell just by looking at the cogs if they are worn. If it seemed to start with the new chain, I’d bet that’s the culprit.

Agreed about the cassette, but also check your indexing. Maybe change the cable/housing if possible.

I’m gonna put a cassette on it (ouch); I think I don’t consider cassette wear often because I don’t keep bikes long enough and I stretch chains so quickly that they don’t ride on the cassette too long

Chains are relatively cheap compared to cassettes. I will change the chain every three or four hundred miles on the MTB(way before it shows stretch on a gauge) which seems to really prolong the life of a cassette.