I had this same problem. Please read some of the "GRUNGE" posts on this very board!!!!
Also read the xp-60 user reviews at:
Harmony-central.com
sonicstate.com
If you cant find the reviews, let me know I will post the direct URLS.
I liked my xp-60, so I took it in to roland to have them fix it. They REFUSED to fix it, telling me it was all in my head. I waited 29 days to get an appropriate response from Roland, but they told me the other people online who also claimed to have this issue were "stupid internet people".
The tech support guy was even a jerk.
So, I told roland too stuff it and returned the xp-60 and got a Korg Triton for 1850.00 US instead.
The annoying grunge sound is when the note fades. Most synths have this, but it is VERY APPARENT on the xp-60, 80, and 2080. It is obnoxious to say the least. It turns a nice sounding synth into crap.
If you do NOT get a satisfactory response from Roland, return it ASAP and get something else.