2004 Hyundai Elantra oil light on and engine knocking

Noises problem
2004 Hyundai Elantra 6 cyl Automatic

My 2004 Elantra was running fine then one night the oil light came on as I was slowing to a stop at a red light, when I came to a stop the light went off. The next morning I checked the oil and it was very low and sludgy so I put in a couple of quarts I had on hand. It was when I started to drive off that I hear the knocking. The knock gradually becomes more audible as the rpms go up till it shifts gears then the knocking stops. I stoped by a gas station and put about 4 qts of oil plus a pint of oil treatment in that day, but it continued to knock. So I took it in to the local lube shop and got the oil changed. Still no change in the knocking. I am worried I may have gummed up my oil pump. I don't see any evidence of a leak, and will be the 2nd to admit (my wife was the 1st) that I haven't kept up with my maint. Like I should. Someone suggested I drop the oil pan and check for loose rods. Anyone else have some advice?(Besides to keep up with my rsm).