Noise pollution can be caused by vehicle, aircraft, and industrial noise. It can also be caused by military or experimental sonar. Noise has health effects on people and animals. In people, it can cause high blood pressure, heart problems, sleep disturbances, and hearing problems. In animals, it can cause communication, reproductive, and navigation problems – they have difficulty finding their direction. Sonar has even caused whales to beach themselves because they respond to the sonar as if it were another whale.