Driven along about 60 kmh and I gets this high whistling sound comming from under the hood. Mostly in the winter time. I was told it could be my ac pump. I use it in the summer and I don't hear the whistle .

 

Not the AC compressor (and it not a pump).

Very possibly a vacuum leak somewhere. Go through all the vacuum lines/fittings to look for old dry rotted lines that have cracks or loose fittings. Throttle body base and air tube fittings as well.