I had a similar issues a few years ago with my JBL speakers in my 01 HL. I found it by sheer luck when i was in the dash. The driver side speaker wires had a small cut in the wires coating and the + and - speaker wires would touch. When they would touch it would cause a static sound until i turned the car off and back on. I ended up cutting the sections out with new wires and never had the issue since. my issue was sporadic and did not happen everyday.... just when the wires touched while driving.
hope this helps