knocking sound cominf from egine cant pinpoint sound it sound like valvels

This is common for people that never figure out where the sound is coming from especially a "knocking" sound. When you hear a knocking sound, the best soluiton is to open the door to find out who's knocking. Just like when someone rings the doorbell. What you'd normally do is to look out the window to see who it is before opening the door...sp, next time, if you hear a knocking sound, open it to see who it is. I hope this helps...