I've had a knocking noise for quite awhile now coming from somewhere around the engine. It only happens when I'm at a constant speed, neither accelerating or decelerating. It's also only really noticeable after about 2000RPM. I took it into a shop, the guy THOUGHT it might be a rod in which case he thought that I would have to replace the engine or the car. I'm being a bit stubborn since I'm a college student and have nothing to spare and seeing if there are any other possibilities. From what I've read, there are numerous things I can check to see if they're loose. The guy from the shop also said that if I use an even heavier oil, I could possibly get away with less knocking and stave off an (in his eyes) inevitable engine replacement. What are my chances?