Quick answer
Whine that follows engine RPM is usually picked up through power or RCA routing. Reroute audio leads away from alternator and charge cables, then confirm the amp has a short, clean ground.
Problem
- Buzz or whine that follows engine RPM through the audio system.
Symptoms
- Pitch rises and falls with RPM.
- Often changes when headlights or fans load the charging system.
- May worsen when phone charges from the same headunit USB.
Cause
- Different ground potentials between headunit, amp, and chassis.
- RCA running parallel to alternator charge cable.
- Poor alternator health or missing engine ground strap.
Fix Step-by-step
- Temporarily re-route RCAs away from power bundles - retest before permanent dressing.
- Confirm amp ground length and point per best practice (short to clean metal).
- On heavy 4WD builds, review charging system health - noise can be a symptom and a sound problem.
Notes
Camera interference users: similar grounding discipline in camera flicker guide.