What is causing this!!?

2008 Tacoma automatic 4 x 4 has been making the “ac expansion valve whistle” sound on and off lately. (It sounds identical to
The videos I’ve watched, but can’t be 100% sure)

It will increase in pitch with acceleration but does go away quickly. Comes back here and there while driving. NO AC is being used while this is happening.

No sound at all on highway, going 75-80. Sound returned as I came to a stop after getting off an exit.

No sound at all today in rain driving around town.

This is baffling me. I took it to
Toyota and they replaced my ac clutch and it did nothing. I’ve read this could be just a common quirk- but I must stress it happens when the AC is off!!

 

I don't see how it is making an "ac expansion valve whistle" when it isn't running the A/C. I would be more inclined to believe that the duct work has a damaged foam seal that is whistling. Esp on a 2008 model (15 years old ).

Does it do it with the fan OFF?

 

Yes. The Reason I referred to the expansion valve whistle, is because that is exactly what it sounds like.

The dealer specked it it was the AC, but the AC was working perfectly the whole time without any issue. So for the sound to be happening when the AC is off, fan is off, I’m really stumped

 

Is the A/C off or are the controls set in the defrost mode which can cycle the A/C even if the A/C isn't ''on?''