Yamaha DTXpress/DTXplorer/DTXtreme

The HH60 on my DTXPRESS 1
Has a minor clicking, noise.  It only occurs when i press down and 
release, when the rubber comes back up.  This sound has nothing to 
do with the electronics.  I hear it when the pedal is completly 
disconected from everything.  Sometimes it clicks once, sometimes it 
clicks twice.  The pedal seems to work fine but is this sound normal?

Mike