Rayer

152000 miles, runs fine pulls strong but.. every now and then a I get a crunch, pop, bang noise when backing up. Car almost feels as though I rab over a can or something. Cannot pin point, originally thought transmission, but not wondering if a rear end issue. Car seems fine all other times. I pull a heavy boat, but only have issues in reverse and not all the time. Anyone have a similar problem or help, thanks in advance, thanks Rayer