Originally Posted by BackwoodsOzarks
If your car is a hybrid, try this:
When parking, let the ICE shut itself off before hitting the stop(start) button.
Next time you start the car, it should not knock.
If this does not work, consider this:
1. we had several owners here, including myself, complaining on eventual rough start ups. engine will shake, even make noise, and then it slowly goes away. It can be anything from mild vibration to major earthquake. It is unpredictable and comes and goes. Last time we had this conversation, no one knows, what and why. We believed, it is one of the PSD oddities.
2. What you describe is more of very persistant EVERY start up noises. What throws me off is that you describe it as "knock". Thing is, everyone has their own understanding of what knock is. Base line being, I believe, you have initial gaps between camshaft and lifters. I do not have information, if lifters are combination of tappets and hydraulic lifter, like Nissan has. They are small barrels with an oil hole at the top, close to camshaft mating lobe. Either way, they have to have very small oil pressure clearance, 0.0031 inch. If either clearance is too big, or lifter is sticky, as in - clogged with carbon deposits, or initial oil pressure is too low, you will have knocking noise at the start up, until metal expands, or oil pressure builds up enough to close the gap.
This leaves me with those guesses: - clogged lifter; - poorly functioning oil pump; - worn out lifter allowing oil to go past, and not keeping the pressure; - worn out camshaft lobes.
I am quite safely assuming, it is clogged lifter. I have fixed MULTIPLE engines with that problem by using Seafoam in oil for several hundred miles, then doing oil change. Last guy we did it had to do it twice, as his Nissan truck was not driven for 2 years and it all got sticky quite bad. Had to do this twice on my son's Infinity also, but it's done. I'd say, cheapest and safest way is to try Seafoam. Pour it into the engine oil, entire can, drive on it for about 200-300 miles, then change oil and filter. Filter will be dead anyway, as Seafom will flush a lot of carbon debris into it.