When I start my 2510 Mule diesel after it has been sitting overnight, the oil pressure light stays on for about 10 seconds or a little more before it goes off and the sound of the engine changes when the light goes off. It doesn't use any oil and runs as good as ever. It just started doing this recently, after it's been started once, it won't do it again until it sits at least overnight or longer. About 1100 hours on the engine. Any thoughts?