When I’m Zwifting and going down hill I put my gears into the big ring in the front and the highest gears / smallest cogs in het back. The chain and cassette makes more noise at that time than with other gear selections. Could this be because the cassette is new (came with the Kickr) and the chain is already 1.000 km old? Any other possible cause?
I ride with a BMC SLR02 Disc 2018 (thru axle) on the newest model Kickr.
It is probably because of the chain line.
Use low viscosity chain lube oil with a portion of PTFE 1 or 2 cycles (1 cycle is 4 crank arm rpm) and a rag to get rid of to much oil.
If this doenst help try pushing the screws on your rear and/or front derailleur very probably it’s because of wrong alignment of your rear/front derailleur.
If you have no problems on the road then it is very likely the rear derailleur position/alignment. play with the screws! When riding on a smart trainer its like changing the rear wheel. The cassette sometimes isn’t in the right position or in equal position like your wheel before in your case like the wheel you ride outdoors.
The longer you ride the less lubrication is inside your chain. Some chains tend to make noise when getting older. 1000 km doesnt sound long but if you rode a lot in the wet then it could be possible that the chain get noisy.