Windows 7 - Static Ticking Noise from USB DAC

Hello everyone - my first post here

I have two DACs, a uDAC2 and an HRT Music Streamer II and both, when connected, give sound artifacts that sounds like a clock ticking. With the uDAC I can mostly solve this problem by not connecting it until my PC has booted up. However, when I surf the web I get random blips that I am assuming are associated with page changes or web ads and also possibly my MS wireless mouse. But at least I can listen to music.

With the HRT this solution does not work at all and it makes music unlistenable. Both devices work perfectly on my work laptop which runs XP. I have done the following so far to enable a solution with no success.

Disabled the onboard sound in the BIOS
installed a powered USB hub
upgraded the USB cable

So what could the issue be? Is it drivers or any of the peripherals that I have got attached. These include your standard broadband modem, printer, powered speakers and two external HDs which contain my music. I initially thought it was them but I have the same issue when using the CD player in the PC.

I've seen this issue discussed elsewhere and one theme is consistent, everyone with this problem seems to running Windows 7 64 bit and I am wondering if this is somehow the root cause of the problem. I suppose that if I partitioned and installed XP I could check but that seems extreme. I'm taking the uDAC2 to a mate's place today. he also has Windows 7 x64 and I'd be interested to see if the same thing occurs.

If anyone here can help solve this I can post it on another forum and help out so many other people.

I also intend to post this in the sound and Audio forum so apologies in advance

Many thanks

Holden