Elantra 2002 intermittent rear brakes noise

A couple weeks ago we bought an '02 Elantra that only has 31,000 kilometers from a local Hyundai dealer. Sometimes when the brakes are applied, there's
noise that seems to be coming from the rear brakes. Before buying the car, I noticed that there was noise at low speed even without applying the brakes. That noise was definitely something rubbing and it occurred once per wheel revolution.
Before taking delivery, the dealer cleaned the rear drums and the noise was gone for a few days. Then it started again, but only when the brakes are applied lightly and the drums are cold. If we apply the brakes again within a couple minutes, there is no noise.
On Monday, the dealer machined the drums because they were not perfectly round. The noise was gone until today. What else could cause that intermittent noise? I don't believe that having the drums cleaned or machined twice a week is the solution.
Thanks,
Ghislain
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It's possible there's some rust or something getting on the drums when the vehicle sits overnight or for a couple days (although this is much more common on rotors than drums). It's also possible the shoes are of a material that lends itself to noise.
If your noise is a squeal type noise and the brakes otherwise operate normally, then it's likely nothing more than annoyance. Find out how much lining is left on the shoes. 3/32" or less means they should be good for a while.
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Today the noise occurs everytime the brakes are applied. The noise that I hear from the back is very similar to the noise that a worn out or defective strut sometimes makes. I know that it definitely is caused by the rear brakes since using the parking brake to slow down the car at low speed causes the same noise. Its more than an annoyance as I also own a Honda and a Toyota and they don't make weird and loud noises when braking. This noise has to be fixed once and for all. .

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