Yamaha DTXpress/DTXplorer/DTXtreme

You don't say which module you have, but I have the DTXpress III and I think I know the sound you mean.  I doubt you can eliminate it.  I have never considered it a big issue.  I am not sure if the sounds improved in the DTXpress IV - only someone with both modules would know.  

If you are considering swapping to the Roland make sure you audition the module carefully - there are some people who don't like the COSM sounds from the Roland.

Keith.