I didn't realize it did this! I was showing wifey a few items from my collection and when picking up the plushie it squeaked, does the same thing when you put it down. That's soooooo cute!
I just tested this with a bunch of the other plushies, turns out most of them squeak! The only one that didn't was the carrack which is bugged and won't allow you to move it or pick it up.
They squeak if you are carrying one and fall flat on your face, too. Happened to... a friend... boarding the shuttle at Orison, in front of a bunch of tooled up players.