WMP chaotic CPU usage

Hello,
I have Windows Vista Home Premium Service Pack 1 ( x64 ).
I listen my music through Windows Media Player 11.
Sometimes when I play X media files WMP it is using 0-3% from my CPU and
sometimes when I play X media files WMP it is using 7-15% from my CPU ( the
same files; this issue is removed temporary only if I reboot my machine ).
( CPU: Core2Duo E6600 )
I don't know why it is using sometimes so much cpu... and I will be very
happy if someone will help me to solve this issue.
Thank You

OK! Very strange!
I opened Windows Task Manager ( As Administrator ) and I open the
"Processes" tab. I select "wmplayer.exe" and choose from the menu ( right
click ) -> "Set Affinity..."... I choose to use only CPU 0 and the Windows
Media Player is working fine ( 0-3% CPU )... if I choose to use only CPU 1
Windows Media Player will work again somewhere up to 10-15% CPU... If I
choose the both of them ( CPU 0 and CPU 1) the WMP will work somewhere up to
6-10%... HMMM!!?!?????

What is this?
My cpu integrity is FINE and it is not broken!

Ok...
Check this out!
In this video you will show how it is used the cpu by WMP while I Set
Affinity!
Just try this link: http://www.microblog.ro/WMP11.wmv

Thank You