Sounds like an electrical short .. I am no expert but it does sound serious enough to take it to a repair shop to have it looked at. Electric problems are notorious for starting fires. Don't use it until you have it checked out.
If you use a power supply, the hissing noise is probably coming from a damaged voltage regulator- caused by failing components. Replacing the unit is usually the best measure, but you could have it checked out by a qualified technician.