I agree with Kevin. Check your crank pulley to see if it is loose. I also agree with not cranking it back up until you get this thing sorted out.

Three possible scenarios to be summed up are

1. Jumped timing= pistons hitting valves causing your noise(this will more than likely be accompanied by engine running somewhat to very poorly)

2. Main bearing or thrown rod= Metal hitting metal internally in the bottom end means bad news big time. This is the worst case scenario IMO. (May or may not run normally)

3. Crank pulley loose= This is the best case scenario of the three. Basically you have a large pulley in the front of the engine that all of your belts are centered on. These have actually been recalled by Mitsubishi to have an upgraded bolt installed or treated and tightened. (may or may not run normally at least until it comes off. Then it will not run at all)

I had to replace the crank pulley on mine because the ribs where the alternator belt is guided decided to detach from the actual pulley itself.

I hope you get this sorted out soon. I know I'd hate to lose the use of my rig for very long.