1999 Pontiac Grand Prix Ticking noise and small oil leak

I recently took my car in to the shop because it sounded like it was miss firing, but all plugs wires and the coil packs were good. Come to find out I had a bad injector. The mechanic said that it had a puddle of water around it which caused it to short out. He said that the water must be coming from a leaky intake manifold gasket. $800 later it was fixed. But when I picked the car up and was headed home I noticed a ticking noise coming from what sounds like the bottom end. I also noticed that it was leaking oil. Since the mech put new oil 5w 30 in it, I new that was too thin so I changed the oil to 10w 30 and changed the filter. Took it out for a drive and it still makes the same noise, and at high rpms it sounds like rocks falling on a tin roof. The mech said he thinks it needs a new oil pump. I think he's full of it cause if oil wasnt being pump I would be able to drive very far. Does anyone no what my problem might be. In dire need of repairing soon. Please help.