I have 2015 Forester XT which has recently had the 100000KM service done and I had mentioned a whistling sound since about 90000Km when I start the car and also during acceleration.

SOURCE: BMW X5 Diesel..When I accelerate

had same problem, mine turned out to be a split turbo pipe.

SOURCE: High Pitch whine during acceleration

First you need to isolate the noise. You don't mention the mileage on the car. Do you have the supercharged engine? If you do, remove the belt for the super and make sure that is not the problem. If you still hear the noise approximately below or from the super area, it is most likely the belt tensioner pulley.
In my car there was a large washer over the pulley (original equipment), as the pulley wobbled on the bad bearings, it would cause a sound like a bad alternator or gear whine getting exponentially worse the faster the engine reved. Now that the part is replaced, you can barely hear the engine idle and is significantly quieter at high RPM.
My car - 2004 Pontiac Grand Prix GTP with 66,000miles.

SOURCE: loud wizzing/whistling noise

i don't know terms or names but i had the same problem. i found for me it was a whistling coming from the black box w/ hose and air filter that is on the right as you look under the hood. I opened it up and re sealed it and the noise is gone. Sorry I don't know the proper names but for me no more annoying whistle while the engine revs.

SOURCE: High Pitch whine during acceleration

Hi Pullerwife,

I have a few suggestions for you,

First of all, check your air filter, make sure its clean, not clogged, and doesn't need to be changed.

I don't know how handy you are, but if you are fairly handy, check the idler pulley bearings, if your not, have a shop check it out, as a last resort.

Power steering pump/fluid being low is also a possibility, but thats usually more of a lower pitched whine then what you describe.

You say once the vehicle is warmed up, the whining stops. Does Weather seem to be a factor as well?

Hope I've helped, and don't forget to rate.

Lazaruselite

SOURCE: Whistle noise when starting cold car

its proberly what they call a secondary air intake pump - what this does is increase the air flow only on cold start up - the colder it is the longer it stays on - if the noise gets louder and you will notice - get it changed - we have the same problem over here on the vauxhall omega and corsa's - bless em got to be GM