Engine knock

[John Mitchell <jmitch@snet.net>]

     I have a sound coming from the lower portion of the engine that I 
can only describe as a connecting rod knock.  It's not noticable when 
the engine is cold but becomes apparent as things warm up.  When I start 
the engine it sounds like everything inside is rattling around, but then 
settles to a regular knocking sound.  If I pull the oil pan, what should 
I be looking for?  The engine is newly rebuilt with about 400 miles on 
it.  Thanks    John Mitchell  76 TR6