Every time I go into rough terrain, specifically bumps or speed bumps, there is a thud sound from the front end. Thinking it might be the bushings but I'd prefer not to purchase without confirmation.
Knocking and squeaking on the Beamers front end usually ends up at the 'bottom-arm rear-bushes'. Check the bushing for excessive movement.
A bottom arm bush failure can be diagnosed on the road by a quick 'stab' of the brakes whilst driving the vehicle. There will be a thud through the steering.
Before stabbing the brakes on the road, make sure the traffic, if any, is not too close!
EDIT - YouTube Video: BMW Control arm bushes E46 or Z4 / Z3 How to DIY: BMTroubleU