My 2004 disco sounds like a diesel when it's cold and really doesn't get that much quieter after warm-up. It sounds like piston slap to me. Is this a normal, a common problem or something else? Thanx.

 

Check for a exhaust leak.

 

some 2003 and 2004 have a problem with the block and front (oil pump housing)misaligned, it effects oil presure and will eventually send the "driven gear" of the pump through the oil pump housing there is a VIN break call the dealer and have it checked. What you are hearing is a valve tap if this is so.