2008 aftermarket CD player install issue

[1slosvt]

I installed a pioneer p80rs in my 2008. All the functions on CD player work fine but now with on low volume or off I can hear what sounds like something cycling on and off. I ensured all harnesses were plugged back but when I wired my head unit I didn't wire up the small plug from the stock CD player which I thought was just the steering wheel control. If anyone has any ideas what it is any help would be greatly appreciated