Kickr grinding noise (v2016)

Last night I hopped on my trainer and it sounded like a box of marbles coming from somewhere “inside” the trainer. Before I tear into it, any ideas about where I should look? I did a belt replacement two seasons ago, so I’ve had the cover off, just wondering if there are common failures that I can resolve.

The noise came on suddenly. Wasn’t there on Wednesday, was there on Thursday. Noise continues when coasting or pedaling, so it’s not my chain/BB/pedals nor the FH. Bike is a SS, so definitely not a poorly adjust derailleur. Spinning manually doesn’t feel gritty, at least not that I can tell.

@AlistairSH Reach out to Wahoo support 1st. They might ask for a video to help diagnose.