Have I broken the unbreakable 4.0L?

With 128K on my '97 sport, I am now noticing a buzzing/whirring noise coming from right around the intake manifold and it sounds internal. It changes pitch with engine speed and I'm not sure what to make of it but I think it's gotten more noticable over the past month. I haven't noticed any loss of power but I'm getting more and more concerned with what it might be. Maybe I'm hearing wrong and the noise is coming from the pulleys or somewhere else but I'm not sure.

check the idler pully, bearings go bad. Mine just crapped out last week. Not a good thing. Check the power steering pump, also you could take it in for a compression check. That will tell you something. Juice

Check for a loose or broken flex plate.

RR3

maybe check for loose manifold bolts?

mine work loose from time to time.

My bet is power steering...

You can test by loosening the serpentine belt. This is done by moving the power steering unit to reduce belt tension. Take out the intake air filter box. You'll see the adjuster bolt at the bottom of the power steering unit (PSU). This bolt only moves the PSU. You must loosen other bolts before the PSU will move. There are a couple of obvious ones, but watchout there are a couple behind the bracket where you can't see them. You need to loosen all before the PSU will move.

Run the motor with the belt very loose, or even removed. Hopefully in this condition the PSU, alternator, A/C, and water pump won't turn. If the sound goes away... it is one of the the turned units. If sound continues you'll have to look deeper into the motor.

Don't run the motor very long without the belt. The water pump is not turning and not pumping water through the motor! It'll go for a couple of minutes without damage. No longer.

The good news is that most I-6 engines run a very long distance before needing internal work. The spinning things bolted to the outside don't last as long. With any luck you'll find the problem outside the motor!

Thanks, guys. After looking further into it I can say with some certainty that the sound is in fact coming from the power steering pump (it was way low on fluid). Mhead, I'll try the belt test tomorrow and see if our theory is correct. What's one of those things cost and how hard are they to put in without jacking up the rest of the system?

I paid around $130 for a pump at CarQuest.It didn,t come with a resivous (sp).Had to swap from old to new.
Also need tool to pull and replace drive pulley,tool is cheap or you can rent.There were 3 or 4 bolts to remove plus the lines and loosen the belt.
HTH
Wayne

Got my rebuilt pump at Autozone fore $89 and it's been great for ~5k miles.