This is from Oz V'hadar L'vusha (I am sure there are dissenting opinions elsewhere):
Here is "Mekoros 73:3" mentioned above, where he writes that he found no sources discussing the matter but reasons himself that it should be forbidden as described above:
I asked Rav Yehuda Herzl Henkin this question. He answered “kolech arev”is not applicable to whistling,but is to humming.