Guys having a few issues with the car atm. Mostly when in reverse and at very low speeds it feels like something is vibrating in the back tyres. And also if im reversing up a slight hill the car will roll forward if i dont give it a bit of gas.
Any idea's?
Im thinking of flushing out the diff and putting new oil in it or is it more serious than that?

Either diff or uni joints would the first thing I check, $50 bucks inlcuding parts per uni joint to get them done.

How do check if the uni's are gone?

im not sure if its a falcon feature but in honda's the car will roll foward in reverse on a hill.. it will do it in drive too if its steep enough.. makes lights fun sitting there rolling fowards and back