Yamaha DTXpress/DTXplorer/DTXtreme

Hello group,
It has been awhile since I've last posted.
Well here is my new problem.  Just yesterday while playing on my 
Dtxpress1, I noticed that everytime I hit the KP60, as I would 
release my foot, it would trigger a second sound.  So as a result, 
for every hit on the kick pedal, it would project two sounds.  It 
was quite frustrating, so I disconnected the wire at both ends and 
cleaned the tips.  Everything seem to work fine now but I would like 
to avoid this problem in the future.  What should I do?

Regards,
Mike