Hello, thanks for your help in advance, i have a 1996 pickup with the 2.7. i purchased the vehicle with a bad head gasket. it ran but coolant was going into the combustion chamber. so yesterday i replaced the head gasket, the job went well with no major issues, i took the head to my local machine shop and they told me it was straight and did not need milled the only thing i did wrong was i did not mark the position of the rotor in the distributer cap prior to removal. after reassembly i put #1 at tdc and installed the distributer so the rotor was pointing at 1. (the manual said to turn engine to make sure it was tdc on compression stroke, due to the large valve covers and lack of a compression gauge i took the 50/50 option) i restarted the engine and the heater instantlly became warm. about 4 minuted into running the engine started to make a rumbeling or knocking noise. the best way to describe the sound is a volkswagon TDI, that i used to have. the sound seems to get a little bit louder as the engine warms up. i took it out for a drive maybe ten minuted of running and the bottom radiatior hose was just barely warm, i am scared to drive it any longer without knowing what is going on in the engine. the temp gauge goes up to about a third and the engine idols smooth and runs good. i have done quite a bit of mecanical work, but by no means am a pro. the noise sounds like it is on the top of the engine maybe something with the camsor valves. it sounds like it is all the way down the engine( all 4 cylinders) it seems to go away at about 3000 rpm. anybody had anything like this or have any ideas, i dont even know where to start.... thank you very much for your help