Quick answer
Whine that follows engine RPM is usually picked up through your power or RCA routing. Reroute your audio leads away from the alternator and charge cables, then make sure the amp has a short, clean ground.
Problem
- Buzz or whine that follows engine RPM through your audio system.
Symptoms
- The pitch rises and falls with RPM.
- It often changes when your headlights or fans load the charging system.
- It can get worse when your phone charges from the same headunit USB.
Cause
- Different ground potentials between your headunit, amp and chassis.
- RCA running parallel to the alternator charge cable where you've run it.
- Poor alternator health, or your engine's missing its ground strap.
Fix Step-by-step
- Reroute your RCAs away from the power bundles temporarily, then retest before you dress them permanently.
- Confirm the amp ground is short and goes to clean metal.
- On heavy 4WD builds, review your charging system health. Noise can be a symptom of it as well as a sound problem.
Notes
Chasing camera interference too? You'll use the same grounding discipline in the camera flicker guide.