Yamaha DTXpress/DTXplorer/DTXtreme

Hey there.

I have been experimenting with my DTXpress and MIDI, but whenever I
plug the MIDI cable to my laptop I get this nasty buzzing noise. I
tired putting an RF choke on it, but to no avail. I also tried
different USB ports on my laptop and nothing! the noise is there
buzzing away over my PA. 

Any one else had to deal with this before? Any tips on fixing it? 

I also have a friend that connects his keyboards to his laptop using a
USB cable to trigger MIDI stuff and he also gets the buzzing noise on
his setup. Is it a ground issue?

Thanks!