Behringer xenyx 502 help!?

[Unknown]

So I went and bought the behringer xenyx 502 and when I got home I plugged in my guitars and was ready to start and when I plugged in my acoustic guitar (no electric) that has a separate pickup to plug Into an amp it has a weird noise that makes the guitar sound weird can anyone help? I will try and see the problem but for now I need help so I know whether or not to go exchange it