High pitch tone behind instrument cluster?

[Roilux]

It's happened twice yesterday, briefly, and I'm stumped as to what it could be. 2004 Tahoe LT, 5.3, 2WD. 170K

City driving, 35 to 40mph, climate control off, driver's window down, radio off. The first time it lasted for 15 to 20 seconds. On the second occurance the tone lasted for over a minute. That gave me enough time to adjust every climate control setting and fan speed wiith no change in tone or pitch. No dash lights illuminated and no codes have been generated. Sunroof was closed.

The whine seemed to come from behind the instrument cluster, perhaps a bit lower. The frequency reminded me of a small bearing failing yet the tone was much softer. When I came to a stop so did the sound. Coincidence? Can't tell as it did reappear briefly again 35mph then it stopped while still at speed. Poking around in the engine bay while at idle doesn't reveal anything. I replaced both front hubs several months ago while doing the GMT800 to 900 brake upgrade.

Today's drive with similar conditions was uneventful. No tone was heard.

Has anybody else experienced this in their rig or have a guess what could create the sound?

 

[Marky Dissod]

The whine seemed to come from behind the instrument cluster, perhaps a bit lower.
The frequency reminded me of a small bearing failing yet the tone was much softer.
When I came to a stop so did the sound.

How did the sound behave AS you were COMING to a stop?
Why do I think it was your afterblower?

 

[Roilux]

How did the sound behave AS you were COMING to a stop?
Why do I think it was your afterblower?

It started as a soft intermittent stutter the first time, remained almost continuous and then abruptly stopped as the vehicle slowed down. The second occurrence was more 'on' then 'off' while at constant speed.

 

[Marky Dissod]

Stumped.
After you give the steering & suspension a good twice over, switch attention to the HVAC.
'fraid those are my best guesses for now.