Funny lines in my photos. help please?

Hi, I shoot with a 40D and for some reason I have these funny lines in my photos. They only appear in a few of them. Any help appreciated. Thanks!

Here's the link because it's more visible when enlarged.
http://farm4.static.fl​ickr.com/3252/...a3c8e​d44_o.jpg

It is very strange and the first time that I have seen this problem. Looks like it may be necessary to send the camera to Canon for repair. Are the lines always there?

No, it's the first time I've seen those lines. Out of my batch of 392 photos, it probably appeared in 4 or 5 of them. I have no idea why.

How strange, they are very regular in the image. Perhaps its the CF, have you formatted it and tried again or perhaps tried another card?

I used a Sandisk Ultra II 2G that I just reformatted before going out to shoot today. Maybe I`ll try a different card and see if the lines appear again but it might be a while since I only had about 4-5 with lines out of my 392 photos.

Perhaps EMI (electromagnetic interference caused by such things as microwave ovens, transmitters, cell phones, cordless phones, computers, etc.). Is there a possibility of some particular source of interference being present whenever the problem occurs?

Ummmmmmm nothing really out of the ordinary. It was a clothing store promotion and there was a DJ present with all his audio equipment. He played music throughout the event but out of all my photos, only a few appeared with lines.