I had a SD9 (off eBay) for about a year and it did not smell noticeably.
One possible cause is patina on the battery contacts (any of the many inside the battery compartments). You need to check all the battery contacts inside the camera ASAP because, if a contact gets hot, heat will flow to the plastic and the plastic will become . . . plastic probably with a smell.
Cleaning the contacts with 100-grit sandpaper or a mill b@st@rd file is not recommended. Paper is about as abrasive as you want to go . . . cotton buds also work well.
SD10/70mm Macro/17-70mm zoom