Look at how the brake shoes are seating into the drum. You can see the wear pattern on the friction face of the shoes. You should see the wear on new shoes near the center of the shoe (lengthwise). If you see wear marks on the outer parts of the shoes (lengthwise), the shoes are not properly arced to the drums. Years ago there were machines that were used to grind the proper contour into the lining. I haven't seen one for many years.
If this is your problem, there is a way to correct the arc of the shoe. You will need to take the shoe back off. Hold the shoe in the brake drum to check how it fits. You should be able to slightly rock the shoe lengthwise in the drum. That is the center of the shoe should contact the drum while the ends will not unless the shoe is slightly rocked or rotated.
If you need to create some clearance on the ends, hold the shoe up lengthwise on a concrete floor and somewhat gently pound the upper part of the shoe with a hammer to cause the shoe to become a bit more arced. Be somewhat gentle because you can go too far and there is not way to go back. You don't need much. Roughly a 32" of rock when the shoe is held in the drum is more that adequate. Don't forget that once the shoe is fully seated into the drum after a few hundred miles of driving that the entire surface will seat evenly with no rocking. What you are after is to allow the shoes to seat properly from the center out. When they are grabbing on the exptreme edges they vibrate and make a lot of noise and may never properly seat.
I hope I was able to expain this clearly. It is easy to demonstrate, but a bit harder to put into words.
