another knock noise ?

[blazer2007]

5 yr. old motor 350/350 stock low miles only driven in the summer, small town mostly in town and on the hiway now and then to stretch it, legs so to speak. Good Lucas Hot Rod hi zinc oil. Anyway I was going to work about 20 MPH and heard a heavy ticking noise,checked oil press. and was 60 psi,pulled over to see if something was hitting but nothing but the noise was down in the bottom of the engine and not a valve train sound ,was heavier than the usual valve noise. Engine ran fine ,nice and smooth,RPM,s were consistent. Took it home and took my Jeep to work,came home and started the truck,the noise was gone. Will try again this morning and see,cold right now 3 below Celsius. I did some reading and the 3 things that came up was rod ,fuel pump and flex plate and someone mentioned looking under dist. cap ,I don,t know why. Couldn,t see anything in the flex plate area for cracks but could be small. I did put in a new carter fuel pump 2 weeks ago when looking for random stall which was the ign. sw. Checked fuel pump with a broom handle and couldn,t hear anything strange. Can these 3 items pump,rods and flex plate be random? I would think the rod knock would be all the time especially when cold. Hope I explained everything.