Got home today and was idling as I checked my phone and heard a ringing coming from the engine compartment.

It sounded like the ringing in ones ears. Hard to pinpoint and as I get closer, it's frequency varies a little bit.

Squirted the belt to see if it could have been a pulley, no change.

Any ideas what this could be?
I've read a little bit and people are pointing to the alternator, but those posts point out that it's in the winter.

Recently changed the spark plugs...could that have anything to do with it?

You can hear the ringing from across the street.

 

Take belt off and try it.

 

Sounds to me like an idler pulley you can take the belt off to eliminate the possible belt noise but if you sprayed it with a silicone spray and the noise is still there it's probably not gonna be the belt I would take a long screw driver or a mechanics stethoscope and put the tip in the pulleys you can get too while it's running obviously not on the pulley but on either the center bolt holding it in place or if it is the alternator try different spots on the housing the ringing will be loud and you can pin point the issue like that and then take the necessary steps to repair it most likely it will be to replace

 

Hmm. I'm not convinced it's that, but since there's two of you; I'll check it out.

I replaced the tensioner last fall, so maybe the bearings elsewhere are going too.

But this sound was like none I've heard. Like if you shot a .223 without plugs and just let the ears ring for a while.

 

My gut is telling me you are hearing the alternator whistle. So I would start there and see where that path takes you. Post up your results

 

Update:

Need help.

After further diagnosis:
High pitch whistle occurs when idling and when rpms are lower than about 1100.

I.e. When I'm driving 20 mph and coast to a stop; I begin hearing the whistle when it dips below that 1100rpm threshold.

Here's a YouTube link to the noise.

 

Did you take the belt off?

 

Getting there tonight. I'm more convinced that it's the idler Pulley now because I cut the engine and heard it fade out.

Will update after I figure it out.

 

So why don't you stethoscope it ? I mean that's how you pin point something like that. Just use a long screw driver or something. It's fast and accurate.

 

Vacuum leak?
Spray a little starting fluid around the vacuum lines with engine running. When idle changes, you've found it.
Typical culprit is PCV elbow on top of passenger side valve cover, but that same hose connects to the back of the intake manifold and sometimes leaks there as well.