Knock from the rear

Very recently and only under hard acceleration I've been hearing knocking from the rear of the car. Any ideas before i get it up on the lift monday?

It could be the exhaust knocking off the rear subframe/diff mount? Its also possible that the bushes that mount the diff and crossmember to the body are worn. Mine are long overdue replacement, I picked up the bushes yesterday from the main dealer, 180Eur for all 4 bushes.

There are also polybush washers that can be used to stiffen up those bushes. Like all polybushes the increased rigidity is usually at the expense of increased harshness. Has anyone on here used these before?

Rear diff bushes I'd say

As above.

Rear diff bushes normally. Check for cracks. Normally on/off acceleration hearing a knock then.