How many miles do you have on your rig? What oil viscosity are you using? Have you tried dumping some engine honey in there (you know - the stuff that you buy in parts stores to stop smoke and knocking, thick as molasses, color of honey) - not suggesting it as even a short term fix but it would cushion the blows your bottom end is taking on start-up to prove or disprove that is what is happening.. Anyone care to chime in on what else it could be? Oil pump etc? I just fully rebuilt my motor after 130,000 hard miles plus massive overheat and crank was well within spec, bearings were worn to copper but still no knocking. When I say hard miles, I drive the a$$ out of this shiny black brick on and off road..Turpin said:Thanks for all the responses. Yes, I do have a deep rattle on start up until oil pressure comes up. It was usually only noticeable in cold weather and would only do it after she sat for 3-4 hours. Now its summer and she rattles on start up and if she sits for about an hour, she will rattle some on start up. I changed the big end bearings that rattled on engine run over. Fixed that! The only other thing it could be would be cam bearing, but seems to be too deep of a knock for that.