1999 Rav4 , rear brake noise

A while back a mechanic put new rear brakes (drums) on my 99 rav-4. After a few days I noticed a squeek in the rear when the brakes got hot. Not a continuous noise, but a squeek that happens with every rotation of the wheel. I had the guy check it and I think he maybe sanded the surfaces. That worked for a few weeks but the noise came back and is getting worse. You can hear it a block away when it's really hot. I think one of the new drums is probably defective (out-of-round). What do you think? The mechanic isn't being very helpful. I haven't pulled the drums to check it yet, but that's all I can think of.

You're probably right. It may be that the drum(s) is too thin from machining and needs to be replaced.