ZDriver.com - Knocking at startup

Hi, I have an 84 300zx turbo and for quite a while now (close to a year!!) i've been noticing a slight engine knock sometimes when i start the car up in the morning (I know thats awful to be just now addressing). It only happens after the car has been sitting for at least half a day or more, and if I give the car some initial cranks without letting it start up fully It starts with no knock or much less (I let the key go before any initial combustion if possible, but usually get a little combustion after the second or third time I tease it with the starter). I'm sure it has something to do with the oil or oil system because when it does knock the oil gauge starts from the bottom and as it moves up to normal pressure the knock fades away. Also when I manage to keep it from knocking the oil gauge starts right at normal pressure. The cars driveability or ability to start in general never has changed after I noticed this, which is my only excuse (be it a poor one) for waiting so long to fix this issue.

I must add that while I can't say this for sure but I think I noticed this right after an oil change, but again thats just a hunch as it's been going on for a while and my memory isn't that great. I might have started out with non-synthetic the first 2-3 changes but I've pretty much always used synthetic 10w-30 in the car and lucas oil treatment if I could afford it, but at one point recently I realized I may have been putting a little too much oil in when I changed it, like a half quart or so, and I definitely thought of that after the sound started.

Another note: I've installed a Megasquirt system (the old computer is completey gone and out of the car) to control my spark and fuel and never really tuned it past normal driving range (i never push the engine past 3000rpm) however I never noticed this problem while I was tuning it and even months to a year after tuning it and driving it around town alot.

So I appreciate anybody actually reading this scattered timeline of my lazy idioacy, but I would love some info on similar issues and where I should start, like using a different oil/oil filter (it will do this with any oil filter even a K/N high performance) or the oil pump or sending unit. Perhaps all the fildling around I've done has caused some slight changes in the engine requiring different oil requirments, but I must re-iterate this only happens in the morning or after sitting for close to a day and add that the car runs and sounds nice at idle and in the range that i tuned it in, but this slight knock problem has been bothering me too much lately and I want to get it on the straight and narrow before I go back to tuning.

thank guys