Advice needed - Zwift Hub: Rumbling chain (or freewheel?)

Zwift Hub with the provided new 9 speed freewheel (or cassette). About one year old. I am pretty sure I purchased a new chain for it too. Unsure of branding.

Now I am using the virtual shifting. I love that. But… It is not always smooth.

I can only use one or two gears on the big ring which lessens the ‘rumble’ grinding. It does not like the small ring even though chain alignment is better.

Shimano 105 front chainring, Specialized Allez Sport bike.

Chain does not measure stretched according to a guage I check with.

Any thoughts? Thank you.

Jim Cooper

I had a similar sound a while ago. Depending on how many miles you have covered the front chain ring could be worn. I replaced mine and all was fine and smooth again.
It could also be the type of chain lub, again I use dry lub/wax for my trainer chain.

@Shaun_Elphick Thank you. Yes, I use a chain wax too. Good stuff.

I use the term ‘rumbling’, yet it is a vibration NOT a noise. Definitely chain/sprocket related.

Does it worse on smaller gears: Ft and RR. Smaller Ft sprocket less wear than FT large.

I’m wondering if my chain was for a 10 speed or something? TIme to repurchase.