You would have to dertimine what, exactly, is making the "thud," and isolate, dampen, or suspend it. This is model and situation specific to your airconditioner.
A loud thud noise in the rear brakes might be caused by stuck calipers or by brake drums that are out of round. You might also have uneven wear on the brake pads.
Another word for thud is "thump" or "thud."
Thud is a noun (a thud) and a verb (to thud).
"I dropped my book and it landed on the floor with a loud thud."
The homophone for "thud" is "thudd."
thud, thud
He hit the floor with a thud.
could be control arm bushings gone bad
you'll hear a loud thud, followed by repairs to your car.
Thud Thud Whoomph
Really depends on the type of thud, so there could be a few reasons; 1. Disks are warped and therefore need machining. (Usually accompanied with a vigorous shake of the steering wheel. 2. Loose bolt on the caliper, can cause this loud thud when on and off the brake. 3. Loose bolt on the strut causing this thud. (although I doubt this but it is possible) And again without hearing the sound it is hard to diagnose. Try to see where the noise is coming from while the car is in a stationary position.
Thud Ridge has 230 pages.