So recently my car has recently developed a weird "tapping noise". Its relatively loud and keeps pace with the rpm level. as in, its regularly paced, and the spacing between taps decreases as the rpms increase.

Low RPM:
TAP.....TAP.....TAP.....TAP.....TAP.....TAP.....TAP.....TAP....

HIGH RPM:
TAPTAPTAPTAPTAPTAPTAPTAPTAPTAPTAPTAP

Eventually at around 3000 rpm it sounds like someone is firing a machine gun, in terms of rate, not in terms of volume. When under the hood, the sound seems to come from the rear drivers side of the engine. The exact location is difficult to determine though.
Anyone have any ideas of what might be causing this?

 

First, tighten your exhaust manifolds if any bolts are loose i recommend replacing the gasket.

Pull one spark plug wire one at a time and listen for a change in the sound. If you pull one plug and the sound is reduced significantly the problem is in the bottom end on that cylinder. (WARNING: DO NOT PULL THE SPARK PLUG WIRES BY HAND! THERE IS A LOT OF VOLTAGE THERE AND A GOOD CHANCE YOU WILL GET SHOCKED! USE INSULATED PLIERS AND GLOVES!) It will not kill, you but it will hurt.... a lot.

Pull the valve covers and turn over the motor by hand make sure all valves are opening and closing equal amounts. You can also run the motor and watch the rocker arms for unusual behavior.

Inspect flex plate for cracks.