High pitched "whirling" sound

For the last year or so, I have been experiencing this crazy, "whirling" noise, coming from under the truck, right behind the cab. It is almost like a high pitched wind noise. Tough to describe.

A couple things about it.
1. Only happens when I press on the gas
2. Generally only happens in morning or cold weather
3. It doesn't seem like a mechanical noise (grinding, clunking)

I have a sneaking suspicion it could be exhaust related, but I can't seem to pinpoint it. The truck runs fine and I don't have any real issues with it other than this.

2001, SR5, Xtra Cab, 2.7 auto, 4x4, 190k miles.

 

You have a vacuum leak somewhere.

 

Carrier Bearing

 

What would be the best way to confirm/diagnose? It does not come from the engine area. It is distinctly somewhere behind the cab.

 

There are plenty of "Vaccum Lines" behind the cab, just sayin.

 

What would be the best way to diagnose?

 

I’m with the carrier bearing. Very common. U can lift the truck on jacks stands. Put it in drive with the wheels off the ground obviously...get underneath and listen around the carrier bearing area. Might need someone inside to give it a little gas or slowly push the brakes. Be careful not to slam on the brakes when slowing down.

 

Get a couple of cans of carb cleaner. Put on the straw. With the engine running, spray all 1/4 and 3/8 vacuum hoses. Listen for the engine RPMs to change. RPMs that go up or down when you spray a particular hose.......investigate further.

 

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A crazy friend with a walkie talkie.