Join Date: Dec 2011
Location: Knoxville, TN
Car: 2015 2.5i Limited Carbide Gray
Generally noise issues with radios (and I have no experience with the Mc system in your OB) are ground related. I would remove the radio from the car but still use the wiring and see if the noise changes. It might be something as simple as ground the H/U to the chassis or it could actually be inside the new H/U. It's good that you found that the noise goes away with a secondary source so you know it's related to just the radio.
Just as a side note Pioneer radios used to be (and some still are) notorious for burning up a pico fuse in the RCA output circuitry if the radio was powered up and an RCA cable was unhooked.