I have had my 2011 forester diesel manual for a month now.. I have noticed a slight whining noise almost like a radio out of tune? in all gears, goes away on exceleration seems present when going along steady and slowing down and stops when clutch is in! 

anyone got any ideas?

Does it do it with vehicle stationary with clutch out ?

open drivers door and check noise with clutch out and clutch in and blip throttle to see if can effect it .

Have you checked gearbox and diff oils since you had it ?

 

Thank you Mr B.  no noise when stationary! clutch in or out when stopped nothing. 

when going along in 4th/5th at around 30 to 50 its noticeable , sounds almost like a radio out of tune and it slowly disappears when I go faster but not there standing stil.. as it was serviced when I bought ive only checked the engine oil..

Might be advisable check/change gearbox/diff oil.

Sounds like gear teeth or bearing issue, possibly teeth meshing if here it more on over run/ gets loader at moment you lift off throttle .

Some noises are improved with better gear oil or if oil level low fill it right up to max .

Noises hard advise accurately without actually hearing it .

what the vehicle history ? high miles, likely been towing ??