when i punch accellerator a clanking in rear end
Might just be a u joint. Then again you won't know until you or someone starts poking around to find source of noise...
Could be a u-joint, could also be a problem in the differential. When were the differentials serviced? The rear one has a limited slip setup so it needs serviced to keep everything working properly. Do what KenF stated, have it checked out before it winds up really costing you.