I have a 98 K1500 with a professional installed JVC head unit and when listening to music on the Aux port, I’m getting a lot of hissing and static that changes with engine speed through the speakers also while driving. I use an iPhone 12 with the Apple branded Lightning to 3.5mm adapter, this headunit is older and doesn’t support Bluetooth or anything else besides CDs and FM radio. What can I look at as the source? Bad grounds or the like? Thanks in advance