See (hear?) attached audio file. Only happens under load on any sort of hill, doesn't have to be a steep hill. I've also been having power cut out (no error) and the occasional error 21. Checked all the cable connections, and they seem to be solid. Any ideas?
Still under warranty? What year/model? If it is under warranty I'd take a video and share it with Rad. There are a few threads about error 21 if you do a search.