Why is transmission making a winding out noise when I hit 40 mph?

Check your power steering fluid.

First thing is to check the brakes, especially the condition of the pads, and if you have worn right through them, the condition of the calipers, and finally the rotors. Sounds like one of these old the key.
In any case can you get back to us with the solution so that others can be helped in the future, thanks.

sounds like transmission is sliping

Could be a Wheel Hub Brg Assy, on front

If you remove the caliper & rotor .You may
feel the bad bearing by hand

No other test than what your hearing around 35 to
40mph.

check for problem drive line "U" joints or cv joints

I had a similar problem on my 2007 RX350 and it was from the plastic gas tank protective cover under the SUV. There is a small portion of the cover that extends forward beside the gas tank, and usually has a rubber piece attached to it to stop it from hitting the floor under the car. The rubber had come of mine so I had to replace the rubber. This stopped it from hitting the bottom of the car at higher speeds. Worth taking a look at?

is this a 4cyl or V6...how many miles??sounds like the transmission isn't shifting to lower gears....is there any warning lights lit on your dash??

take it to a different mechanic its a bad speed sensor

Find a quiet empty stretch of road. Go 50 mph, put the trans in NEUTRAL and shut the engine. If noise is still there, swing car left and right to detect noise differences. Could be hub or axle bearings. Not engine or trans if noise is still there. Hope this helps

It's a step-by-step process. If it only happens on acceleration then it is a drivetrain problem. Start verifying from the outer cv joints and go in from there