The jack on the side is an earphone jack. So you could listen to your outgoing security message.
The sounder or sounders {I don't know it it has one or more in parallel} is a Piezo type.
Most likely glued to the case. Maybe they just came loose and are floating inside the case.
Though Piezo Sounders are fragile. They may have cracked as X10 doesn't have them in a shell just glued to the case.
You can buy Piezo sounders but we would have to find a suitable replacement as X10s are a high voltage very small current type.