75ZT Community

I have a ZTT 190.
This is the problem, which started a few weeks ago:
When the car gets to 50mph and above, a rhythmic thumping noise can be heard, which speeds up and slows down with the car. I can't feel it through the steering wheel.
The exact location of the noise is hard to pinpoint. I thought it was coming more from the rear, the garage felt it was coming from the front.
Before I took it into the garage, I rotated the wheels. That made no difference. I also checked the weights, they all look present and correct. There are no obvious defects with the tyres.
I took it into the garage, and they have been out twice in it. Their findings were inconclusive. I was told that the rear left brake caliper is sticking when it gets hot, but is fine when cold (It failed it's MOT and part of the rectification work was freeing up the caliper. This was in March). I was also told that the front right wheel has some 'run off'. Solving either of those things might cure it, or it might not, I was told. Their feeling was that either the wheels or the tyres are the problem, but dismissed tracking.
What would be my best course of action? Does anyone have any other theories? Is a sticking brake caliper a problem for the model?
The cheapest option I think would be to start with fixing the brake caliper. Any advice or guides on doing that would be most appreciated.

On the basis that brakes are fairly important irrespective of whether this is causing the problem it requires fixing.

As it is speed related and not feeling it through the steering wheel would indicate to me that it is not the front of the car.

I would look at the exhaust system and whether it is vibrating against something. Is one of the rear wheels out of balance and is the spring and shock OK.

Best of luck