Help me figure out this sound

My truck (‘98, v6, 200k) has been making a high-pitch humming noise when I have my foot on the gas. It’s distinctly different than my regular engine noise. It is most noticeable (and quite loud) at 65 mph when I’m just barely giving it any gas (going slightly downhill on the highway) but I can also hear it at lower speeds in town. The noise stops as soon as I let off the gas. Plenty of transmission fluid, no lights on, brand new tires and brakes. It’s driving normally other than the noise. Any guesses?

 

Welcome to TW...Can you get a video?

 

Have you looked underneath for Robert De Niro?

 

Yes really hard to get an idea with no video, can you sit there and get the same sound by revving the motor to what the rpm’s are at 65mph? I would possibly think vacuum leak, make sure all your intake is in good shape. Back to the 65mph noise, what if you’re going 65 and just quickly let off the gas, is the noise still there?

 

Here is a video: https://youtu.be/5b3NJ5slYys

@oldtimertoyota the noise stops a second or two after I let off the gas. I can't hear the noise if I rev the motor to the same rpms, but the regular sounds of the engine could be covering up the noise.

ABS light is on, has been on since I got the truck (and definitely before the unknown noise began). Doesn't give a code.

 

This is an interesting one, I’m hoping others chime in to possibly get some more ideas. I’m still thinking an intake issue. When did you first notice this noise, had you had any work done on your truck?

 

What transmission is in the truck?

How old's your carrier bearing? If it's only when you let off the gas, I'd try to rule out any weird cause coming from the driveline/trans/transfer case/rear diff. Fluid good in all of those?

 

@oldtimertoyota The noise started soon after I got new tires and replaced an ignition coil.

@Red_03Taco its an automatic transmission. Not sure how old the carrier bearing is. I had the pinion seal in the rear diff replaced in the winter to fix a leak and it doesn’t seem to be leaking oil anymore.