I was going down the highway today and noticed my oil pressure started dropping off. Pulled over and checked oil level and it looked like it was way down. Filled it up then got it going, oil pressure stayed low. I also started noticing what appeared to be a faint knock or rattle. Would this be from a bad oil pump or bearings all of a sudden going out? Noise comes on when revving up to about 20 - 30 mph. I have always had good oil pressure at idle and at speed so not sure if something just failed.