Audio problems

Hi,

I hope that someone can help me with this, I have an audio problem that is difficult to explain.
First of all my OS is windows 7 ultimate 64 bit, and my Motherboard is ASUS P6TSE.
My sound card is M-Audio Delta 66, with a 2 X 2 midisport USB.
All of the M-Audio drivers are up to date, so I do not believe that is the reason for the issue that I have.

After boot up I always load up ITUNES straight away, and all is fine.
What I find is that after an hour or so for no apparent reason, the audio starts to distort and wine, and occasionally the speed of the track slows down and speeds up.

On have noticed on the ASUS Web site that these BIOS updates are available, I don't known if these are applicable.

Realtek ALC1200 Audio Driver V6.0.1.5859 for Windows 7 and Windows 64bit 7, and Intel Chipset Inf Update Program V9.1.1.1014 for Windows XP 32bit/XP 64bit/Vista 32bit/Vista 64bit Win7 32bit/64bit.

I have re-installed Windows three times for other reasons, but this issue appears each time.
PLEASE HELP ME!!!!!
If there are any questions I will be happy to answer them, if it means getting an answer to this nightmare.

regards to all