Help with strange noise

[Hano]

Hello!

I've got an -08 Legacy Wagon and recently it has started to make a strange noise. The noise is like a whine or humming and it happens when accelarating or coasting. I have the four speed automatic and the noise is present on all gears but it starts to become noticeable when I go over maby like 50km/h. Also the noise seems to be louder when I start driving and becomes more quiet after a while but doesn't fully go away. The noise does go away however if a put the car on neutral. The car is due to transmission oil change soon but can it be only that? Patient in photo.

[Greenmamba]

Is the transmission fluid at the right level, checked with the engine running, in Park?

Does the noise change if turning right or left? Quite possible to be wheel bearing all else being equal.

[Hano]

Haven't checked with the engine running..

The noise doesn't change when turning. Would the wheel bearing noise stop when putting the car on neutral while moving?

[Greenmamba]

Subaru auto transmissions must be running, in Park. If you have been checking with the engine off, the marks on the dipstick will be way off; you may have very low fluid which could explain the noises.

[Mr B]

if goes away in neutral it gearbox output side, could be low oil and lets hope it is but also highly likely be shaft bearing .
 

[Hano]

Thanks for quick replys! I will check the oil level correctly and let's hope that is where the problem is.

How big and expensive job is it if it's the shaft bearing?