Emissions or Oil pump or other?

Driving at about 75 miles, I heard a slight brushing noise, turned off radio and heater, still heard noise and then "Check Gauges" message beeped on - off - on. Noticed oil pressure had dropped to lowest point, pulled off, oil about a quart low, added oil. Started back on the road went about 5 miles, brushing, grinding noise started again only much louder, pulled over right away and engine light came on. Had truck towed home. The handbook says engine light is emissions.

What could this be, my oil pump went out or something more or less serius?

Thank you for the help and advice.