The truth remains though, that noise is a powerful source of stress. It is true that some sounds may be found to be soothing and joyous, such as certain music or the sound of songbirds. But we donít need an opinion poll to find that for the vast majority of us (even those that cherish their Ford Expeditions) vehicle noise pollution is not considered relaxing, but instead is annoying, or at the very least, unwanted. And research shows that our body perceives noise that is considered ëunwanted or intrusiveí as a threat or warning. And even if the noise is not a threat or warning, biological changes still occur and strong stress reactions are triggered. Stress reactions include the release of several stress hormones, changes in heart rate and rhythm, rise in blood cholesterol levels and digestive upsets. It becomes easy then to see how vehicle noise pollution can be traced to a multitude of stress related illnesses.