Knocking sound, please help!!!!

I have a '98 cavalier 2.4L and recently just purchased the vehicle. It has been upgraded to an extent and is a beautiful show car. But recently in the last 2 days the car has been making a knocking sound. I have taken the engine apart the best I can without much tools and have had no luck and also washed the engine to see if something was possibly fludded and still no such luck...any suggestion are helpful at this point. Please help