Popping? How? When?
Are you sure it's the hatch and not a rear suspension problem?
I occasionally get a noise during acceleration and braking from the hatch when I don't close it firmly enough to latch it. If you only hear it when driving over a swell or bump, the body may be flexing, the latches may need adjusting and the hinges lubrication. It's also possible the inside plastic door panel isn't fastened properly.