Yamaha DTXpress/DTXplorer/DTXtreme

Hi fellow pad bashers,
I have a pretty simple problem to put forward to the group,
(Bearing in mind that I am quite new to the world of E Kits)
I am experiencing a volume issue with the Kick Drum sound.
I have noticed that If I hit say about ten consistent single beats, 
one or two notes are heard at a higher volume or depending on how 
you look at it, eight are too low and 2 are OK.
The volume setting in the modules display indicates 127,
I have adjusted the gain pot on the rear of the actual rubber pad 
which as expected, increases or decreases the volume.
This erratic Kick volume is evident on all factory kits,
I have not edited any of the factory volume settings on the Kick.
I have to be honest the Kick volume seems a lot lower than the snare 
& Tom's, the Kick seems to be at maximum ?
It's as if the pad is not working consistently ?
Am I thick or am I missing something ?

Cheers !