Well, I really know nothing about the p's, but on the older versions there has always been two sound wires, connecting in one end to the circuit board, and in the other end to a round metal sound piece. If you'd open up the tamagotchi and check for sound wires, it is possible that you'd find that one or more of them are loose, not soldered in place.
If that's what's causing the muteness, it is possible to carefully solder the wires in place again. That is however a quite critical operation, and it also requires the correct equipment.
I don't even know if the p's have the same sound system as the older tamas, it's just a guess. But you might want to open it up anyway and look for broken parts, then write here what you find, and maybe someone more experienced with color tamas can help you.
I'm sorry I can't be of more help, but good luck!
