Annoying noise only at 48 kHz

[Ellipao]

I'm encountering a strange problem I hope you can help me with.
I've just built a new computer (i7 860, 4GB ram) which I intend to use also as a DAW with Cubase, virtual instruments and audio recordings.
I installed the same audio card I had in the previous PC, Terratec EWX 24/96, which has always been very good for my needs and which actually forced me to install Windows XP x64 instead of the planned Win7 because of the lack of drivers.
Everything is working fine, but I can hear something like a scratching noise when playing audio at 48kHz, not only in Cubase but also in any player. It does not always occur in the same "place" while listening and is not always the same, becoming more or less loud in an apparently random way, especially with certain sounds. The very same audio files do not produce any noise when played on another computer. No noise at all also with any other higher or lower sample rate of which the card is capable (32, 44.1, 88.2, 96).
I already tried changing all possible settings in the audio drivers (Asio buffer size, DMA buffer transfer latency) with no results at all. As soon as the sample rate is set to 48 kHz (changing Cubase project settings or playing a 48kHz audio file) the noise starts.
What can be the reason of such a strange and annoying behaviour?
Do you think it could come from (or cause) some hardware damage?
Thanks for any help.

 

[Whale Bone]

Is there an external device connected via S/PDIF or is there an internal or other sound card that is interfering? My Echo Mia would always have to use my dbx 386's clock if it were on. Something about master/slave clock behavior or settings?

 

[TimOBrien]

That would be my first guess, too (a clocking problem)

But I'd wouldn't use 48k in the first place.
The only reason to use 48k is if you're doing video where 16bit/48k is the standard output
or if you're using hardware (adat's or SBLives) that only works at 48k.

 

[Ellipao]

Thanks for your answers.
I have gone through further investigation and I found out that the problem seems to be in the EWX Asio drivers.
Using a wav file player I noticed that if I choose, in the player's "audio driver for playback" settings, the EWX Analog Driver, everything is fine. As soon as I choose the EWX ASIO driver I start to hear clicks and pops, while playing the very same audio file.
Clicks and pops seem to occur randomly, sometimes they do not occur for a while, sometimes they are lower or louder and so on.
Sadly, inside Cubase I can not choose any other driver than Asio.
I tried re-installing the EWX driver and after restarting the PC I had two whole hours with no noises at all, making me think I had solved the problem, but when I started the computer the following morning I discovered I was wrong.
I also noticed that computer activities (hard disk and USB access, opening/closing of windows and so on) produce some noise in the loudspeakers, which is independent from the volume setting. I installed the audio card three slots away from the video card (which is fanless, btw) and almost ten cm above the PSU (which is on the bottom of the case); no cables at all near the audio card, as well.
I really do not know what else to try.
Maybe I should roll back to XP 32bit, but the system seems to be rock solid and is taking full advantage of its 4GB RAM. I'd really prefer to find a solution without having to spend a day reinstalling everything...