I personally think its the headunit because it only makes the noise in the front speakers AND while its in CD mode. If its on radio, there is no noise with the front or back. After I start the truck, I get the sound of the CD starting and reading. Then after that noise goes aways, it fades into a constant humming/buzzing sound. Then when I switch the source to radio, it goes away. Keep in my, this is with the volume all the way down so that I can be sure of what I'm hearing.