TOPIC: Where can I find noise inspection

There are methods for sound reduction on windows. It's done all the time around airports. I see it here in Los Angeles around the airport all the time.  It usually involves a secondary set of window panes, mounted on the inside. In Los Angeles, it was part of a noise abatement project as the result of a law suit I believe.
You may be getting more noise on the upstairs rooms due to height above ground.  Buildings and other things may be partially blocking the sound on the lower floor but are not doing so on the upper floors.  Here in Los Angeles, they build high "sound walls" along the freeways to block most of the sound from traffic from reaching the houses adjacent to the roadway.

Do the noises coincide with high winds?  If the so, the wind might be blowing past some kind of void causing the whistle sound.

Thanks for your replies. ( I just come back from vacation - with no noise )

Dana, We are now thinking of install sound absorption curtain, or so called acoustic curtain. Do you think it could help?

John, The noise stays there all the time no matter there are high winds or not. One day there are concert outside of our building,  I can clearly hear louder sound from the concert in my bedroom than my living room. This makes me think it might be some issue with the windows in bedroom ( quality issue? or maybe they are not installed properly? ), But I don't know how to prove it.

Sound curtains may help, time will tell if you install them. I know the double window systems seem to work. I've been in these houses near the airport with a big jet flying over and it reduced teh noise considerably. I think it would be impossible to totally eliminate it.