Sarah, we had the exact same problem on our Rebel 32R. My wife kept finding screws breeding on the floor. On closer look the aluminum support bracket at the bottom back of the microwave that was supposed to support the thing had all of the screws missing. Not one of them actually made it into the microwave base. This allowed the microwave to "bounce" off the support bracket and the entire weight of the microwave was pulling the cabinet above it off the walls. What I did was remove the microwave (there are two long bolts that go straight down from the base of that upper cabinet, you;ll have to remove the thin wood that forms the base of the cabinet to get at the bolts. Once the microwave is down, I resecured the bracket to the wall, but I also added another piece of 1/16th" aluminum angle to the side of the cabinet so that one flat side was against the shower wall (your layout might be different) while the other flat side supported the cabinet. I managed to hit the internal supports of the shower wall but be careful of the plumbing. Once all that was done, I rehung the microwave (quite heavy) and made absolutely sure that the screws on the back bracket made it into the microwave base. We just returned from a 6000 mile trip and had no further problems. Sorry I can't send any pictures but our unit is in the shop getting maintenance done. On another note, check your refrigerator as well, ours pulled out on the first trip.
