Where does my problem fall? This is annoying!

[alfa147x]

http://photosbytwesh.com/clip.mp3

also along with that sound it sometimes cuts out as well!

Thats what my left speaker sounds like, randomly
I havnt been able to notice a pattern as to why but its random

My receiver is a Aiwa AV-D97 + 2x 3-way bookshelf speakers

I wonder if its because my speakers are 6Ω while I can only choose between 4Ω and 8Ω on the receiver

I have tried an iPod as another source as well as another cable this also happens when I use TOSLINK from my Macbook Pro

Thanks for any help!
Alfa147x