legacycentral bbs

its a bit hard to describe the knock. it definetly knocks on idle and under load like i say until it warms up a bit. it recently has gotten alot louder, and can be heard in the cab. the only way i can descibe it is when i rev the motor it knocks away the same as the normal subaru rumble. had a lube ...

can anyone help with this one?

i have a 1990 single turbo ej20. when cold it knocks quite loud.
but after it has warmed up it seems to either go away or quietens down. a mechanic mentioned piston slap but not sure.

any ideas?