It's pretty damned simple, actually.
Lube up the latch.
Yep, that's all. Mine squeaked a LOT, drove me insane. I tried everything from adjusting the bump stops to keep the door from moving at all when closed, to propping something against the door from the inside.
Turns out all I had to do with dab some grease on the latch, and the squeaking went away.
EDIT: didn't see post above mine.. so in other words, I agree