Loud Humming Noise!

I have a 99 Tacoma 2.7 4x4. The engine has 265k miles, but it runs strong and has been very reliable for the last 65k miles. Awhile back it started making a loud humming sound. It sounded like the powering steering pump was giving out, so I replaced it with a brand new one, and the damn noise wont go away. Then I was told that it could be the A/C compressor because when the A/C is running the noise gets louder. New A/C compressor and still the noise is there. At my local Toyota dealer, the mechanic said that it was either the Power Steering pump, but its brand new, or it was the A/C compressor idler/tension pulley. Well, it got a new Idler/Tension pulley installed yesterday and that noise is still there. I just contacted the same Toyota mechanic and he tells me that it could just be normal wear and tear. I know the truck has age, but the engine and everything else runs great. I have no other issues but that noise. Can someone please give me some more ideas as to what else could cause a loud humming sound?? It gets especially loud when the A/C is running. Any info would be greatly appreciated. Thanks.

 

One possibility is that the power steering reservoir screen is plugged.
When they put in a new pump, they reuse the reservoir, and never check the screen.
This is a widely reported phenomenon, and easily fixed be removing the reservoir (3 bolts and a hose), back flushing and reinstalling, preferably with a new o-ring.

 

I would try running it without the belt for a second just enough to hear if its in your pulleys pumps or internal timing area?

 

Thanks guys for responding. I never even gave it any thought about the reservoir screen, I will check it out. Also, when the A/C compressor was installed, we used the same pulley. I never once thought about replacing the pulley as well. Now that you bring it up, it could be that A/C compressor pulley. Ill check both when I get off work. If its something with the internal timing, is that an easy fix, or costly and timely?? The reason I ask about the internal stuff being costly is because I am selling the truck, and the buyer wants me to fix that humming noise before he pays me. So if it turns out to be something like the internal timing and its expensive, then the price just went up! Again, thanks a lot guys for your advice.

 

The only way to check the ps screen is to take the reservoir off the engine, empty it and shine a light up through the bottom. Free if you do it yourself.

 

I plan on doing it today. I need to get it fixed up, so the sooner the better. Ill keep you guys informed for future reference.

 

Got it taken care of. Turned out to be the bearing in the A/C Compressor pulley. Changed it out, and NO more NOISE! Thanks guys.

 

Good on ya!

 

I have a 1999 tacoma 2.7 4wd with 122k and it starts to make make a higher pitched whistling/humming sound coming from the rear area of the truck when i go about 20mph and over.. Anyone know what it could possibly be? I haven't a clue