Walkman Sound Cuts out when touching the door

I just received my third WM-550C. It sounds all just like it should, but the actual sound is very finicky. It seems that the door being pressed against the machine with nearly any amount of pressure causes some mechanism inside the Walkman to cut the sound feed. Now in a normal case, upon opening the door or pulling the door away from the machine, it would cause the same effect. I noticed that the one I received had a piece of foam at the top of the inside of the door. None of my other models have this, and I’m beginning to suspect that the previous owner used this as a solution. Of course I assume if that were the case the foam must be starting to break down by now, thus, the problem remains. Any ideas on why it’s doing this and how I can make it stop?