Mpc 500: Sound problem

I recently got an mpc 500, brand new. I just finished installing new pads (fat rubber pads) and i closed it all correctly. Now, as i push A6 to get a hi hat sound, it is not sounding right! I get a distorted hissing Sound, even with another pair of headphones. I feel as if something is wrong.. Any of you have any experience with This?

Thank you. I'll do that.. Wanna say 'do the right Thing - bon soir