Noises are hard to diagnose by remote control. Does it make the sound all the time and all speeds? Is the sound soft or sharp? Deep heavy metal clunk, light tap, or somewhere in-between?
To help with info, get a stethoscope, or chunk of garden hose, or long screwdriver or broomstick and put it to your ear, moving the other end around on the engine to pinpoint the source as close as possible. Let us know what you find. Diagnosis before disassembly. A bit more known history of the engine may also be helpful.
David
PS: If it makes you feel better, the last knocking engine I had was a loose harmonic balancer. One bolt re-tightened and the knock was gone. Hopefully yours is similarly simple.