Yamaha DTXpress/DTXplorer/DTXtreme

Hi All,
I have noticed that my TP65S snare is starting to double trigger 
around the edge (but not the rimshot area) and is fine in the middle 
of the pad. None of the settings have been changed (rejection or 
location etc). If I swap it for a TP65 tom pad the problem goes away. 

Can the Piezo trigger come lose? how is it fixed in place?. I looked 
at OGD's pics on it, and it looks like a sticky pad? but I'm not sure.
Would like to get some info before I open it up. Thanks in advance.