UR 44 clicking under heavy use

Hi All;
I have a UR 44 with the latest drivers installed.

Setup is:
Win 7. 8 core AMD at 4.2 gHz, 16 G memory, all software including operating system on SSD.
almost all of Windows disabled, no Internet accessability, no anti-virus software. Only pipe organ emulation software executing.
all physical devices disconnected in other USB 2.0 ports.

Under heavy usage, that is a lot of data transfer, I get a loud click / pop through the speakers. I have increased / decreased the buffer sizes but with no improvement. Replaced the UR 44 with another UR 44 and many other tweaks but to no avail.

As a test system, I have a smaller cpu ( 4 core AMD at 2 gHz, 6 G memory ) but with Firewire and an AudioFire 8. I never get any popping??? go figure!

Any suggestions as to what might be the issue???

much appreciated…