Whistle Sound from Air Vents in 5th or 6th Gear

I've been combing through the forums and have not been able to find a relevant discussion, apologies if i missed something obvious.

I have a 2018 TRD Sport manual.

When i'm cruising at highway speeds (5th or 6th gear), i commonly hear a soft whistle-like sound that will come from the air vents when i have my foot on the gas. The sound will disappear if take my foot off the gas. To the best of my knowledge the symptom does not appear when in lower gears.

Does anyone have any idea what may be the cause of this? I'm not even sure if this is normal and intended. At this point i'm just curious if this is anything to be troubled about.

 

I'm in for the responses...........

 

vacuum leak?

 

Want to say howling rear diff.
Could be described as Really low pitch whistle kinda sound.

 

Some people complain about a whistle from the LCAs. Might be related to that

 

Strange. Maybe hit recirculate air button and see if still whistling?

 

Can definitely confirm that it’s a relatively low pitch whistle as far as whistles go.

 

Will give this a shot and report back.

 

I heard this in my truck today when the wife put the air on. She is going through the change and you can hang meat in our living room she keeps the house cold. But yes I heard it today but I thought it was coming from the radio. I am interested to hear from others. It is not a steady whistle, just now and then