Does it occur both idling in the driveway and while driving down the road? If only when driving down the road, does it sound the same when coasting vs in gear? Any change to the sound when the brake pedal is applied? When you say the noise speeds up the faster you go, do you mean it changes to a higher pitch? From an oooooooh to eeeeeee sound the fast you go? Is there any change to the sound when using different gears, or if a manual when the clutch pedal is pushed in?
One thing you could try, get a length of old garden hose and use it as a stethoscope to better isolate where in the engine compartment the sound is coming from.
Other possibilities
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Parts that vibrate can sort of sound like a squeal. The cat heat shield is one of the most common causes of vibration sounds.
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Vacuum leaks can make a squealing sound. I’ve had that happen before from a vacuum leak at the valve cover gasket. Not a soft squeal, really loud, but only happened when the engine was warm. Use the garden hose, maybe it will point to a vacuum leak somewhere. That kind of sound will tend to diminish if you temporarily bump the throttle, and be loudest with your foot off the gas. PCV valves can sometimes make a vacuum sourced squealing sound.