Back and forth

[baksa]

Yesterday I replaced whole clutch set with new one and I thought that I solved problem but it's still there, only less noticable.
Problem is that in low speed, in second or third gear (most noticable), when I suddenly release gas pedal, car jumps a bit forward-backward on the move, and when I hit gas pedal after that it jumps again and I hear a knock on the back of the car floor. I also changed rubber part which was near to brake, it was damaged.
What else should I consider to solve this?
Car is manual M50 520i.

[DaveVoorhis]

Bad subframe bushings?

[Morgenster]

ditto on the bushings. Mine are due for replacement and I get the 1st and 2nd gear stumble a lot.