Background Noise

Hi,

I've just set up samplebox for the first time on a raspberry pi 3. I followed the recommended install instructions on the Make It page, installing the image as the only OS on the PI. I've downloaded sample-set instruments from the site and am using a USB stick to load them onto the PI.

The samples are playing, and I can switch between the sample-sets on the USB stick, but there's background noise on all of the samples. It kind of sounds like there's a saw wave always playing behind all of the notes, I've tried different headphones/speakers to rule that out as the cause.

Does anybody have any idea what might be causing this?

Thanks
Alex