Reviving this thread - I think I have this exact problem. Just bought the Tacx Neo 2T, have a grinding noise and have landed on this thread. 
I will check tomorrow if it is resolved by using the old cassette, but then the problem is: This can’t be a sustainable solution if you have only 1 bike that you use outdoors too. Changing the cassette every time doesn’t seem to be very appealing…
Would the grinding noise eventually go away if I just kept the new cassette on it, or would it just ruin my chain?