Today, in the middle of nowhere (actually a rest stop 25 miles south of Bellingham, WA), when going into reverse, my 07 automatic made the worst sort of metal on metal grinding sound. Like the screeching sound of train wheels on a track. It didn't do it in Drive and I tried it a couple more times in Reverse. Did it again each time, but with lessening intensity. Notheless, I aborted my family's planned visit to my ailing father in hospital in Canada. I called my Dealer's service dept. Only one person on staff on a Saturday. After holding, I told him the situation. He was puzzled but said they'd have a non-Mini rental for me. I never made it down there (NW Mini) as there was an I-5 closing accident. I called the service guy and told him that I wasn't going to make it and would have to wait until Monday. Thing is, after we stopped for lunch, it went into reverse without any noise. And proceeded to operate fine for the rest of the day.
Any others with a similar situation? Any ideas?

This is the second transmission issues with the fam on a weekend (last one, it was stuck in 5th gear) and now I have 0% faith in the vehicle for long distance road trips.
Thanks, all!