I have a Kia Sorento 2.5 diesel. I have noticed an unusual rattling noise a bit like when you shake a paint aerosol can. It occurs at around 1900 revs or 30mph in third gear, 40 mph in fourth gear and 50 mph in fifth. The noise disappears if I increase or decrease speed in the appropriate gear by 5 mph or change down or up a gear. Has anyone any idea what is happening? I think it is mechanical as I don't think it is a rattle from something loose in the engine compartment.