Whats wrong with my bmw x5 ?

i have a 02 bmw x5 4.4i, whenever I cruise for like 45 mins continous I start feeling that when accelerating then pressing the brakes till a stop I feel a bump in the car as if somthin has hit it, on occasion its strong and on occasion barely felt ? what is this ? a gear problem or a torque convertor one ? is it serious ? there r no alarms or msgs that appeared on the car's computer ? so what may it be ?

sounds like cv joints

Possibly common joints on drive shaft.

CV joints possibly if it occurs while turning the steering wheel when it happens.

its time for the new 2007 x5

Rear subframe rubber mount maybe worn out. When you speed up the car, the subframe mount will stretch, and when you slow down for just bit, the stretched mounts will send the rear axle to up direction, causing it to hit the car's frame.

How hard you get hit is depending on how far the subframe rubber mount stretched down direction throughout acceleration procedure, and the problem is more observable in low rpm zero 30 miles range Car rear axle uses H shaped frame, so you have four of them and parts could run around $50 each. Removing them will require some kind of pressing tool so I could service this in the dealer.

it is most likely a programming issue. take it to your local dealer and have them check faults. if none are present, then they'll most likely flash your egs transmission module .
It may also be your driveshaft coupler. it can because a jolt throughout load reversal or acceleration.