The World Health Organisation has guidelines for noise levels that can cause increased stress levels and cardiovascular problems as a result. A general annoyance level is 35 decibels. Disturbed sleep is put at 42db and chronic night-time exposure leading to cardiovascular problems is put at 50db or above (click picture or comparision here).
Research has shown that noise can increase the level of stress hormones such as cortisol, adrenaline and noradrenalin within the body. The longer these hormones are at high levels in the body then the greater risk of leading to heart failure, strokes, high blood pressure and immune problems.
The WHO has produced noise maps which show the noisiest European cities whilst the EU has issued a directive that says that European cities with populations above 250,000 must produce digitised noise maps to show where traffic and other noise is at the greatest level.