A-500 Pro & Zipper Noise

I just got an A-500 Pro yesterday, hooked it up (USB only) & installed the driver.  That part of it went ok.... and if it is triggering an external module (routed thru Sonar), it works fine.  However, when triggering a softsynth, there is an audible crackle / zipper noise when I press a note down, when there's a note off, and when I move any of its controllers.  I have another keyboard hooked up (also thru USB) & have no such issues.  I tried hooking the A-500 up thru MIDI, but the MIDI out jack didn't seem to transmit anything!
 
I'll be troubleshooting this today as time allows.  Any ideas on where to start?
 
edit: I'm using X1d Producer, Windows 7 64 bit.
 
thanks,
 
greg

RME RayDAT running into a Yamaha O2R (via ADAT lightpipe). I think you nailed it though. My card's buffer settings were set to 32 ms (which worked fine on my M-Audio Keystation KS-Pro-88) and worked fine for the Casio Privia PX-130. But I had to up it to 128 ms to get rid of the zipper noise on A-500Pro. That's disappointing. Is that something I'll have to live with if I keep it? thanks, greg

Ugghh... well, Jim.... as I already knew.... you're a fricking genius... and I'm a bonehead. Sure enough, it was in a USB-3 port. I plugged it into a regular USB port, set the buffer back down to 32 ms & it's fine. No zipper noise. Thank you sir!

is it to do with the improved transfer rate then Jim?

thats interesting, they say it's backward compatible.

Jim saves the day again. :)