engine knocking/ticking

I recently replaced the front wheel bearings, so I hadn't paid attention when this sound began to occur. Anyway, its more of tapping type of noise. I checked the oil, it appears fine. Could it be a loose spark plug, a lifter? It seems to be coming from the front of the engine. Its not noticeble when I'm in the car with the windows up. It taps faster when I rev the engine, even when I accelerate I can hear it if there is no traffic. I can get a video up if that will help.