Hi I have a Sony F717 that I just bought and it seems to have faint lines in the photos when taken at higher ISO settings. I was wondering if this is normal or not?

I have included a photo at ISO 100 and ISO 800 Here:

ISO 800 w/ lines:

www.bytephoto.com/photopost/showphoto.php?photo=57826

ISO 100 w/o lines or very faint lines:

www.bytephoto.com/photopost/showphoto.php?photo=57825

Any advice would be awesome thanks guys!