Weird whistling noise after I turn the truck off

[stevj]

I have traced my noise to the radiator cap.
Here's what I think is happening.
When the engine is shut off, coolant stops flowing but the engine is still giving heat to the coolant, which raises the pressure a bit more.
This causes the relief valve in the radiator cap to open ever so slightly to vent that slight overpressure to the coolant catch bottle.
Once the system cools and the coolant contracts, the fluid returns to the system from the bottle.

Steve

 

[Simann]

This whistling is not a pressure whistle from leaking fluid or vapor. This is a whistle only heard inside the cabin, only when shutting truck off. Mine has been doing it for at least 30K miles, quite regular now even while driving. A/C works fine so I doubt its TXV, rather, the amplifier for speakers. My brother is an engineer said something like capacitor discharge in amplifier? Who knows.

 

[My1stHemi]

This whistling is not a pressure whistle from leaking fluid or vapor. This is a whistle only heard inside the cabin, only when shutting truck off. Mine has been doing it for at least 30K miles, quite regular now even while driving. A/C works fine so I doubt it’s TXV, rather, the amplifier for speakers. My brother is an engineer said something like capacitor discharge in amplifier? Who knows.

The capacitor is an interesting thought. I’ve had my amplifier replaced under warranty for what I thought was ANC related issues but I still get the whistle/whine.
Do you ever hear clicking/static emanating from the upper rear speakers in the headliner? I do and cannot replicate or trigger the issue. It happens randomly and regardless of the audio source or if the radio is on or off.

 

[kapinallinen2]

A/C works fine so I doubt its TXV

My TXV has been whistling from day one, ac works fine despite it.

 

[Simann]

I don't see how an HVAC part could be causing the sounds I hear from my speakers. Its is no doubt from the audio system. People on the other line while talking on phone have heard it. Sounds like a whoopie cushion sometimes. I will take it to an audio shop, see if replacing speakers and an amplifier may fix it.

 

[kapinallinen2]

I don't see how an HVAC part could be causing the sounds I hear from my speakers. Its is no doubt from the audio system. People on the other line while talking on phone have heard it. Sounds like a whoopie cushion sometimes. I will take it to an audio shop, see if replacing speakers and an amplifier may fix it.

If it is coming from the speakers, while driving, then yeah, nothing to do with HVAC.
Post an update after you figure it out.