iHome iP9 - Audible hum

When I listen to either the radio or my iPod on low volume on the iP9, there is an audible hum and it occasionally surges the hum sound. It happens whether or not the WiFi is on, and there are no fluorescent lights, computers, cell phones, microwaves, etc. nearby. The only variation is when the iPod is plugged in to the dock the hum is louder, but does not go away when I unplug the iPod. You can drown it out by increasing the volume, but I don't want it to blast me awake. Does anyone have any ideas? Are they all like this or will a new one be fine if I return this one?
Thanks - Z