All types of singing and Whistling along with air through the windpipes have positive psychological effects on us.  When signing our body releases endorphins, endorphins are produced by the central nervous system and pituitary gland, they are chemicals released by the brain that make our body "feel good".  Singing in front of a crowd at an affair or in a karaoke setting, naturally builds confidence which has its obvious effects of confidence building along with other of general well beings.  But, from all types of singing, choral singing seems to have the most dramatic effect on people's lives  Studies have shown that people who sing in choirs rated their lives as happier than people who sang in other formats.  From personal experience I can say that when I volunteer at a nursing home i see the seniors who take part of the choir they seem to be happier and more lively.  These residents also have proven to show less signs of anxiety and depression levels.  

Whistle while we work... the phrase originates from the slave days. During that time period, kitchens were separate from the rest of the house , they had a seperate location as they posed fire hazards and also were considered a place for the help was.  In an effort to keep the enslaved help from eating the food of the family and their guests while they carried it in from the kitchen, the help were required to whistle.  But with time the catch phrase "Whistle while we work" grew to become something more positive.  In the original Disney Movie, Snow White and the Seven Dwarfs, the Dwarfs sang the song "Whistle While we Work" and in fact pyschologists say they were right.  Although Whistleing as we work doesnt always help our surrounding environment but it certainly helps us be more chipper and work better because we are enjoying the time. 
The famous musical. "The King and I" portays whistling as a mechanisim of hiding fear.  The song,"I Whistle a Happy Tune" suggests that if we whistle noone will know what we truly feel, in this case noone knew Anna was afraid. I feel that whistleing is a great stress reliver as well as a good way to lower anxiety and i find that when i whistle while i work the work just seems to pass by much quicker and seemlessly.