sounds like by the age of it, making a noise like that, it mite be ready for a trade in or a scraping, i know you can can get attached to your baby but a new model always makes the blow easier until you wonder what you were ever doing driving round in that rust bucket.. if you really want to keep it, lift the bonnet and check its oil level.. im taking it that you are female to let the car get this rusty, the oil is measured with a dipstick, give it a general look over, and try to locate the location of the noise, take it for an and MOT to find any problems that you couldn't find. hope this helps.. oh btw, what car and model have you got? certain models have the same problems with age, you've gotta think of a car like a pet.. you gotta treat it right look after it, and you cant expect it do be jumping loops and doing 180mph when its 13yrs old