1998 Pontiac Grand Prix engine knock

I recently replaced the starter on a 98 pontiac grand prix gt. The old turned out not to be bad but was extremely loose. The next day the car developed a loud knocking soundin the motor. My intial thought was the starter I replaced it with was bad also and making contacting with the fly wheel. Replaced it w/ old starter and problem continued. I checked the fly wheel and could not find any noticable cracks so that leads me to think maybe the engine has a broken rod. Car cranks and still idles and has power in the motor however on acceleration the knocking speeds up also. The sound could be described as a wrech thrown in a metal bucket and shook. Anyone have a guess what could be causing this problem. Is there a simple way of telling if it is a rod? Thanks.