Bad Bucking

[nc211]

Anyone ever experience the following?

Going in reverse, foot off the gas, then slip the car out of reverse without foot on the brake "just coasting backwards", when car disengages from reverse into neutral, the back end clunks and bucks badly. It won't do this if I have my foot on the brake. I'm wondering if a rear suspension bushing is bad? I've got new motor mounts and transmission mount. I have no other "classic" symptoms of a fully worn out bushing, like clunking or bucking, under any other driving format. It almost feels like it's in the differntial too? It doesn't do it if I'm rolling forward and then slip it into neutral though....just backwards. I'm stumped...