A couple weeks back, my 96 ES300 started making a high-pitched, shrill, metallic squealing sound while driving at high speeds. The sound tends to kick in around 60-70 mph, and fades in and out. Seems like the faster I drive, the louder it gets. It's unclear where it's coming from. It sounds like it's coming from the front end maybe, but the louder it gets, the more it sounds like it's coming from all around me, like the entire car body is acting like a shrill tuning fork. It can also happen at lower speeds, 45 mph+, if I'm driving on a rough road. I tried getting it to happen while in park and revving to high RPMs, but it wouldn't. So it seems like it happens only while on motion, or at least while in gear.

I looked at the belts, don't see anything obviously wrong. Fluids are topped up. There's no way these are my brakes? (I do need to replace a few of them soon, but they usually squeal only when braking, and they don't sound like the problem sound I'm hearing.) Almost sounds like two pieces of metal grinding on one another. Anything else I should check before I take it to a shop?

I managed to record the sound. It's muffled in the recording, but louder and more shrill in person:
https://vocaroo.com/1os1gnLApLMa

 

Not sure what that is. Sorta sounds like wind noise, or tire noise, or could be something completely different like worn/dragging brake pads. Can you get the sound to change with throttle or when pressing the brake pedal?

 

Too low of a pitch for brake squealers. Could be a vacuum leak. Can you tell where it's coming from?

 

Generally it's louder the faster I'm driving. I'll see if there's a closer relationship to the actual throttle by stepping / letting off it faster while driving. I'll try the brakes too (carefully at least, at 60+ mph lol).

At lower speeds, it sounds vaguely like it's coming from the front, but at higher speeds, it sounds like the entire car frame all around me is squealing. If it was a vacuum leak, could I hear it in park with my foot on the gas at high RPMs? The sound happens only when the car's actually in motion / in gear, not in park.

EDIT: I did just put in a new engine air filter a couple weeks back. I wonder if I cracked the air intake hose or something by accident. I just looked at it right now, don't see any obvious cracks.

BTW, I've got a BlueDriver monitor + OBD scanner. I can leave it plugged in while driving and have it log stuff. Anything in particular I should look for in the logs?

 

Any progress? I've had worn-out front wheel bearings make similar noises... I recall hearing such while getting on the freeway and within certain higher speed ranges without feeling any obvious handling issue. Also I recall it would sometimes correspond to steering (right or left curves at speed). Tricky to diagnose for a novice like me.

I'd wager you'll want new wheel bearings all around.

 

I was about to suggest wheel bearings too.
I would not rule out the brake squealers. Might be this particular brand has a higher pitch.

And while this is remote, there have been pranksters that stuck a deer whistle on a car to make the driver crazy.....just like this is doing.

(I miss college....LOL)

 

Difinitely check the wheel bearings, if for no other reason ensure they're good to go.

 

Months later, the problem seems to have cleared up. Or at least, I can't hear it anymore. I figure there are two options:

Option 1: the problem went away spontaneously, whatever it was. Or, it's decided to take a breather before the part fails catastrophically.

Option 2: I might have had a thin gap above my passenger side window, and wind was whistling loudly through it, when driving at high speeds. I was out driving 70-80 mph recently, and the shrieking noise started up. I rolled down my passenger window a few inches to see if it made a difference. It sounded like the shrieking noise went away when I did that, but I honestly couldn't tell with the roar of the wind through my now-open window. I rolled the window back up, and the shrieking noise came right back. I did notice that my window motor seemed sluggish. I tested it when I got back home and parked, and the whir of the motor sounded lower than usual, and the window was moving up and down slower. So maybe that motor's on its way out. And maybe the window wasn't rolling up quite as much as it normally should--just barely less. So then I pulled the window up as far as I could with my hand, while also using the window motor. Then I took the car out a couple more times at 70-80 mph, on a bunch of separate occasions. No shrieking noise. Hot damn. So I'm guessing there had been a very thin sliver of space between the top of the window glass and the rubber along the car body, of just the right width to turn my entire car into a giant, obnoxiously loud kazoo. Physics is weird.