my 96 ford transit is making a horrible noise each time I start it like a rattling grinding noise I cant hear exactly where its coming from but sounds like inside the bottom of the engine , after about a minute sometimes a lot less it stops and goes away until I turn of the ignition and start it up again , the van seems to run ok still though I have noticed that the cooling van goes on as soon as i turn the key and stays on ... really puzzled please help