what can cause drum brakes to pulse

[bluebombersfan]

I had new rear brakes and drums done about 7000kms but they have a slight pulsation to them, it's not the pedal that pulsates though it's the brakes themselves. I took it back to the shop that did them about two months ago and they said that there was nothing wrong with them. I took it to another shop for a check-up on something else and they said the rear brakes needed some work, on the paper it says advise rear shoes and machine drums I declined there service just because I had already paid for the new brakes that were on.
Anyone have any tipps on what can be the problem. I don't understand why brand new drums would already need machining.

 

[AllanD]

Sounds like the drums need to be cut.

AD

 

[bluebombersfan]

I was thinking of taking the drums off and getting them machined, but I get the feeling this might be a temporary fix.