How to Fix Alternator Whine in Car Audio | 12 Volt Outlet

That high pitched whine that climbs with your RPM is alternator noise. It is one of the most common calls we get, and it is almost never the alternator's fault. Noise is getting into your signal or power somewhere. Two quick tests tell you where, and most fixes cost nothing.

Sounds likeWhine that rises with RPM

Usual causeBad ground or RCA routing

Test time10 minutes

FiltersLast resort

Find where it gets in
Fix it in order
Grounds
RCA routing
Filters
Mistakes

Find Where the Whine Gets In

Start the engine with the music paused. If the whine rises and falls with the gas pedal, it is alternator noise.

Now unplug the RCAs at the amp and leave it on. If the noise stops, it is coming through the signal path. If it keeps going, look at the amp's power and ground.

Alternator whine diagnosis flowchart for car audio — Two tests point you to the right fix.

Fix It in This Order

Free fixes first. Grounds and wire routing cause most of the whine we track down. Filters come last, after you know the install is clean.

Five steps to fix alternator whine, free fixes first — Free fixes first. Filters last.

Step 1-2 Check Your Grounds

Your amp ground should be short, bolted to bare metal and tight. Sand off paint, use a star washer, and keep it under 18 inches. At the radio, use the harness ground wire, not a random screw under the dash. Our guide to bad grounds shows what a weak one does.

Step 3 Keep Power and Signal Apart

Run your RCAs down one side of the car and the power wire down the other. If they have to cross, cross them at a right angle. Cheap RCAs with thin shielding pick up more noise, so quality cables pay off here. Our guide to running power wire through the firewall shows the route we use.

From the bayRCAs zip tied to the power wire are the most common cause of whine we see. Moving them often fixes it on the spot.

Top view of RCA cables and power wire routed on opposite sides — Power on one side, signal on the other.

Step 4-5 When to Use a Filter

Still hearing it after the free fixes? A ground loop isolator on the RCAs at the amp breaks the loop that carries the noise. If the whine was in the power path, a noise filter on the radio's 12V wire cleans it up. For a step by step on signal side noise, see our RCA noise and ground loop guide.