can anyone please explain why my car might rattle/clunck when driving in low speeds/gear but goes away after picking up the pace

 

welcome to the forum
we are not mind readers for the most part
Speed, road conditions, when it started etc will help, miles on car- repairs done and things already looked at will narrow it down too

could be an axle bearing a/k/a cv joint, hear that in hard low speed turns and mid speeds when its the inner bearing, a lot of noises come from there!

Could be thunk as trans shifts- with broken front and or side motor mount broken
give us a little hint here!

maybe the egr system is clogged, 99s need to do the cleaning procedure by removing intake manifold every 75kmiles for sure!

 

look at the sway bar bushings and end links
The upper and lower front control arm bushings are prone to wear as well
that will thunk on bumps and potholes

 

because as speed increases so does other noises which might make what you are hearing harder to detect.

Can you be a little more specific as to what end or side of the car you are hearing these noises?