After about 20 minutes of driving a thumping noise appears sounds like it is in the rear, when the brakes are applied or the traverse slows down it gets loader. If I stop at a light or brake/slow down to turn the noise stops. Brakes and rotors have been checked and are okay.

Hi. The noise id definitely coming from your parking brake. You will need to break down both sides and inspect everything. There is more than one reason to cause this failure. Check the shoes, are they in good condition ( check that the pad material isn't separating from the backing plate)? Are the springs attached and in good condition? Ask a person for help. Have a friend engage the parking brake and release. You will check the shoes and see if they have fully returned. If they don't you must determine if the failure is related to a cable or seized lever against the shoe. Take your time or you may spend more money than you need to. Please let me know if there is anything else. Good Luck.

rear hub-- tire faulty--tire balance -bent rim --brake rotor//caliper suspension worn need to remove wheel and inspect

Are the drums new? Have they been machined?

I have a bmw x3 that is making a banging noise when slowing down or crawling in traffic. it has just passed its mot had new front brakes and handbrake.
has any one experienced this or can help me to solve this problem.

Check your wheel bearings.

A BEARING MAKES A GROWELING NOISE.
BRAKES WOULD MAKE THE NOISE WHEN APPLIED.
THUMPING MORE THE FASTER YOU GO, LIKELY A TIRE THAT IS SEPRATING.(NO LONGER ROUND)

It is probably the flexible rubber brake line that runs from the axle to the metal brake line on the frame. When these become old they don't allow the brake fluid pressure to reduce when the brake is released.

i recently had 4 tyres fittede and tyre company had crossed threaded one stud so forcing brake disc to be loose, hence when handbrake applied got thump from brake area.

You say you hear the noise when you "slow down". Does this mean you hear the thumping noise when you let off the gas and let the car coast to a stop or only when you are applying the brakes to decellerate?
If you only hear the noise while applying the brakes then I would assume it has something to do with your brakes. The first thing that comes to mind would be rotors that aren't true or warped which could make a thumping sound.

Do you feel any vibrations in your foot when it is applying pressure to the brake pedal? If you do feel a sort of pulsating feeling then it could very well be your brakes making the noise.

I hope I was of some assistance,
AadoubleA

yes my cv axles had to be replace cause of the same thing but when you replace one side you need to do the other side at the same time cause when 1 goes bad the other is not that far behind . i know from experience