2002 Subaru Forester High pitch hum

It is REAL easy for noises to be transmitted, so don't overlook things in the front. Front wheel bearings will sound like an airplane engine, and will often get louder or quieter when turning slightly such as when changing lanes. A rear bearing can do that too, but front ones are more common because of the drivetrain weight they have to hold up.

Look for a mechanic who has a "Chassis Ear". This is a set of six microphones you clip onto suspected noise sources, then you drive the car, listen with headphones, and switch between the microphones. By determining the loudest one and moving them around, you will zero in on the noise source.

Caradiodoc

All those things are possible, but you're going have to listen next to the source, either with microphones or by running it in gear on a hoist.

Not all wheel bearings change sound when turning. That was common on older cars with pressed-in bearings. Most cars now use bolt-on assemblies. Even when their sound changes, you can't be sure where the noise is comming from. The only way I found to tell for sure was to run it on a hoist and listen with a stethoscope. One will sound a little rumbly so you won't be sure, but the other one will be obvious it has a problem. You won't hear the noise by ear that way because there is no weight on them.

Gear noise is usually a pulsing howl. Here again, it might not do it on a hoist when there is no load on it.

Your best bet is the Chassis Ear. You might be able to rent one at one of the auto parts stores, but a lot of people won't even know what you're talking about. The guys who drive the tool trucks like Matco, Mac, and Snapon can order them. The old version has 6 microphones with wires that must be carefully run to avoid hot and moving parts. The newer version has two wired mics and four are wireless. The old version, as I recall, runs around $100.00.

Caradiodoc