Whining Noise from Hood When Turning on Lights or AC/Heat

Hello friends! Been lurking here a minute, but finally had a question that I couldn’t solve by the already existing threads..

my (2007 tacoma prerunner sr5) has started making a whining noise under the hood only when you turn on the lights or the AC/heat, and then the sound increases when revving.

I’ve already put a brand new serpentine belt on it as I saw that as a solution in another thread but this didn’t solve the issue.

thanks!

 

Alternator will whine louder as more load is applied to it, and as engine rpm increases. Up to a point, it's normal. A heavy duty alternator will whine louder, like a police cruiser's. Beyond that, could be bearings. I had one replaced in my Taco at around 150k. Bearing noise can be similar to normal alternator whine, but louder. If it IS the bearings and it's been whining for a while, I would change it. Feel it (carefully) after driving. It will be warm, but shouldn't be hot. The bearings are on the front and back of the center shaft. The pully side usually fails first.

You will know it's out when the battery red light appears on the dash. You can still limp home on the battery, if you're close. Depends on the condition and charge of your battery... which is now in question.
I've never been stranded by an alternator, but I've never had one lock up because of bearings either. Being on the serp belt instead of a seperate belt like it used to be, will work against you.

 

Could be it then! Any ways to verify before I replace it?

Could this be signs of it going out soon? It’s been going on for about 6 months now.

 

On a GM vehicle I disconnected the alternator plug to see if the whining went away or lessened and it lessoned being disconnected but I've never done it with a Tacoma.

 

Good idea! I’ll try that before doing anything drastic

 

(Starts truck up) "Honey, did you hear something weird when I started the truck?"

Lol

 

If the unplug the alternator test doesn't pinpoint the issue you could try this. Remove the belt, check everything the belt touches. Idler pulley, tensioner pulley, water pump, etc. I'd bet something will feel off. Every pulley should spin freely, no play up down in out side to side. No notchy feel. I'd start with the alternator. Still, check them all. Maybe both alternator & ac pump are causing issues.