01 cherokee knocking

i have a 2001 cherokee 4x4 with a 4 liter, it has about 120,000 miles its always been a good truck, no problems just normal stuff. just recently though its devoleped what sounds to me like a rod knock i hope to god i am wrong. i hear it the most when i stand just behind the drivers side tire and listen close.

any suggestions as to what else it could be

check for a cracked exhaust manifold... do it where it Y's together.. very common.... If you can't see a crack look for black soot on the pipe