2004 Tacoma V6 26k miles 4x4 auto tranny.

Here's the deal on this odd noise.

When the engine is warmed up and at idle (about 700-750RPM), the noise doesn't sound like it's there. If I turn on my headlights, I start to get this squeaking or chriping noise. If I turn on my KC Daylighters with the headlights, it gets even louder.

If I turn all accessories off, and kick in the A/C or defroster, I don't get the noise. If I crank the wheel while not moving (again putting the engine under some load), no noise.

If I shift into "N", no noise. If I put the motor under a bit of load by shifting into "D" and sitting still w/ foot on the brake, no noise.

The noise only crops up under electrical load. This is NOT coming through the speakers, nor is it any sort of RF noise. I tried to isolate with a piece of tubing as a stethoscope, but had zero luck. All I know is I get a noise under electrical load, but not under any other load.

Under normal idle (lights off), the noise does not appear to be there. Alternator? Belt? Something else? I need a hand on this one, as I don't know what the likely failure mode here is.

Thanks!

 

I'm not 100% sure, but I would say it is your Alternator. But I'm sure other members will chime in with more help.

 

I had that same problem with my old 4runner. It turned out to be a bad diode in the alternater. Have a battery or auto electric shop check it out. I took the alternater out myself and it costs $30 to have them repair it.

 

Thanks for the input. I hope some more folks chime in. I think I'll let it do it's thing until it craps out. I've got the 7/100,000 platinum warranty on this truck (Toyota contract), so they can fix it on their dime.

 

You should have it looked at before it craps out because if it truly is a burned out diode it will continue the burn up diodes because now all the rest have more load on them. Second of all when you have a poor alternator it puts more strain on your battery and makes it likely to fail. Schucks, Autozone, Napa, and many other places will check your whole system for free. However it is cheaper to have an electrical shop fix your alternater rather than buy it new.

 

Good point, but guess what? Noise isn't there anymore. It may have been the unusual cold (freezing and lower, in SF Bay area == NOT normal) + noisy belts. But I will look into it more, as you suggest, just in case. Thanks!