Squeal under hood 5 secs noisy, 5 secs quiet

[C6Pilot]

I recently purchased a 2013 1500 Sport with about 23k miles on it. After the engine is up to temp I get a high pitched squealing under the hood. It happens while driving and parked. It doesn't change if I engage the A/C.

The strangest part is that it's almost perfectly timed, 5 secs of squealing and then 5 secs quiet, constant rhythm while the truck is warm. It's loud enough to hear inside the cab driving with the windows open. Super high pitched and super annoying. Anyone have a clue?

 

[darthdzl]

Fan clutch weirdness maybe? I believe the Hemis still have clutch fans, don't they?

 

[C6Pilot]

I did stare at the fan but didn't notice any change in rotation speed by eye. The fact that it's perfectly rhythmic at idle tells me it's not something like mechanical slippage. It's too evenly spaced. Someone on another site mentioned vacuum leaks. I suppose if there's a pinhole in something it may whistle once it pulls enough vacuum and then it stops until the vacuum overcomes the pinhole again. I can see that being rhythmic but it doesn't sound too easy to find because of the engine noise and air currents.

 

[twooldfarmers]

I did stare at the fan but didn't notice any change in rotation speed by eye. The fact that it's perfectly rhythmic at idle tells me it's not something like mechanical slippage. It's too evenly spaced. Someone on another site mentioned vacuum leaks. I suppose if there's a pinhole in something it may whistle once it pulls enough vacuum and then it stops until the vacuum overcomes the pinhole again. I can see that being rhythmic but it doesn't sound too easy to find because of the engine noise and air currents.

use a piece of tubing such as anold piece of garden or heater hose as a stethascope to try and isolate the area of the noise. You can feed that hose down amoungst all the hardware and belts

it could be a simple bearing in one of the idler pulleys on the serpentine belt

 

[C6Pilot]

Another weird "clue". After it begins its squeal cycling at idle, if I rev the engine a few times it tends to stop the squealing cycle. I've done that and it goes away until the next time I drive it.

Does anyone know if I can safely disconnect the alternator power? Maybe it's a charging cycle turning on and off putting a load on the alternator.