High pitched noise issue using external audio device with DDJSX

Hi all,

I recently purchased a DDJSX and I love it. However, I have plugged my laptop running Ableton live into one of the channels using a standard headphone (3.5 mm) to RCA cable and I'm getting a slight high pitch noise through the speaker and headphones. I'm also having the same issue when I plug my iPod in as well. I've set the input select to 'line'. When I change it to 'phono' the high pitched noise is very loud. Am I using the wrong type of cable or is it something else. Basically I would just like to know the best way of connecting a laptop running ableton to a mixer.

Cheers guys

Conor