Whistling Truck

My '07 Tacoma Double Cab recently started making a sound that I've never heard before -- a sort of whistle. Seems to be coming from somewhere in the vicinity of the passenger-side rear wheel well.

I've posted an audio track of it here. It varies in loudness in the recording whenever I pass by a fence close to the street and the sound is reflected back, but in actuality, it's a pretty steady volume.

Any clue on what is causing this musical accompaniment?

 

Are you sure it's a whistle?
I'd maybe put it on jack stands and then put it in gear.
I'd want to see if it's wind related, or mechanical related.

Sounds like a weird idea. But you have to start somewhere.

Does the sound change with speed?

 

Howdy. I'm pretty sure it's a mechanical whistle. Kind of a long squeak to my ear. The sound stays the same pitch regardless of speed.

 

Rear axle on jack stands and put it into gear.
Chalk the front tires.
Grab a buddy and get to listening.

It sounds dangerous, and can be if you aren’t being cautious and careful.
But it is 100% a diagnostic method.

 

Thanks for the suggestion.

 

I heard the video...
take your rear wheel off on that side & look at the brakes....
Something that loud, should be obvious...

before you do that, do any off-roading?
Seen guys on here bend the seal protector at the rear axle diff pinion seal.
If so, bend it back..
My guess probably not in the you joints but What TNShooter said would def help isolating it vs taking wheel off & looking without isolating first..

Even if you dont own jack stands & you have a legit floor jack only.
If you have plenty of space & youre smart about it, safety wise, you can still lift the rear by the pumpkin.
Put it in drive using a buddy.
& inspect from behind...
So if you lose the jack, truck roles forward, not over you...

 

Thanks for the input. Much appreciated.

 

Sounds a bit like a disc brake wear indicator.

 

Disc brake wear indicator, eh? That makes sense. Thanks for the suggestion. I'll post back here when I finally uncover the answer.