I just bought 3500 Highcountry early this month and also having the same problem...besides this, water leak from driver side's sun visor, GPS not working since 2nd day , was told it wad due to GPS antenna failure, mentioned about whistle noise to service adviser and was told it was also causing by bad antenna... I am currently still waiting for the new antenna(3weeks already..)
I noticed the whistle sound is coming from windshield where mirror located/or front part of the sunroof. When I drive the car very early in the morning, I won't be able to duplicate the noise, but during mid day after I drive for 10/15 mins, I can start to hear it, and it is loud, that sounds like the old school stovetop water boiler..
Anyone here had the problem solved?
Sorry for the broken English.
Ken