I replaced the wires, plugs, pcv, etc.

There is a low noise engine knock. As the engine heats up the noise slightly increases. Sounds like a diesel. Nothing coming out of tail pipe. No lose of power.
Before I changed the plugs. The plug on the drivers side in the back of motor I could touch it and feel a hard knock. With new plug, wires and correct gap, I feel nothing.

Should I continue to drive it or take to a mechanic? Or does this engine sound like this with close to 200,000 mi?