I have been investigating a similar issue with Ued 2.
On my main setup, it is using a lot of context switching, and eats 50%
It seems to be an issue with my sound setup, rather than me having an AMD. I have checked 5 intel PCs and they all do the same, but not as high (They are mostly Realtek sound chips).
I think it may actually be My ATI graphics card, not liking being used on an nForce 2 motherboard with onboard sound.
Ued3 works fine on the same setup, with no CPU overhead !
A quick test
Try editing the UT2004.ini and switching the audio in the editors section to "UseAudio=False".
If that helps, try a different sound card (my next step), or see if newer MoBo chipset or soundcard drivers are available.
The program "Process Explorer" by "Sysinternals"
www.sysinternals.com is able to show you the "Threads" working inside Ued. Use that to help you.
The only "help" I have been given so far on this is "get a faster PC", and thankfully 1 reply for a % reading from other peoples PCs.
http://www.ut99.org/viewtopic.php?f=5&t=3877&start=0
NOTE. Our problem is similar but may not be the same.