i had the "bees" noise as well, and noticed it the very first time i got the vehicle up to highway speed. the dealer that i bought the truck from was absolute CRAP so i took it to another dealer. they replaced the cowl and resealed the windshield. i went 13,000 miles before i heard it last week.
i keep my explorer in a garage at work, and at home, so she rarely gets out in the sun. i did park my car outside one day in the heat, and the "bees" noise came back, for just the drive home. after it cooled down in the garage, i took it back out, and the noise did not come back.
heat definitely seems to be a factor.