Static

Don't know where to start. I just installed a new sony head unit in my Yukon. I bought the wire harness but didn't hear anything out of the speakers when i had it connected to rather than messing with it i just ran wire direct from head unit to the speakers. I noticed that they is static (still have the stock speakers) What can i do to stop this? Is it cuz of the shitty speakers?
thanx for any help