I purchased my refurbished XSP in November. I have flown 14 flights since then with no issues until this past Sunday (Jan 14). One of the motors feels like it has sand in it when I rotate it by hand. It's rough to turn and feels gritty or "lumpy" as though it had lots of dirt in it. It does not. The coils inside are clean and shiny, and I can see nothing in there that would account for the feel. It appears this happened somehow with the XSP just sitting in the case since I didn't notice anything when I took the propellers off after my last flight on Sunday. I noticed it last night while checking the Master Airscrew propellers for looseness (separate thread on that). What the heck could have happened? Nothing about the flights was unusual and I didn't hear any strange noises from the motors.. I have not dropped it or otherwise abused it. Weird! But, I can't fly anymore until this gets fixed. I have e-mailed Autel so we'll see what happens.