Sometimes when I start my z I hear a single knock just before it starts. Any ideas? She runs perfect, just seems weird.

 

Video with sound??

 

i hear a knock too when starting!! same issue here

 

"...just before it starts." Just before the starter begins to turn the engine, or just before the engine begins running?

Probably need more clues to get a good answer. Mileage? DE or HR? Mods? Where the noise seems to be coming from? Engine cold or hot?

 

I have a rattle just as it starts.
I suspect the timing chain tensioner.
This only happens on initial startup after extended shutdown period.

 

before the engine starts running...04.5 DE...68,800 miles...cold...

 

You are absolutely right with the chain tensioner. A lot of DEs in the maxima community have this too. Some of them have installed an oil primer that gets oil pressure up to about 30psi for 10 seconds or so max before they start the car, which makes the chain tensioner tighten up and makes the knock go away.

OP not saying this is or isn't your problem, but it's a known DE thing when the chain starts getting looser.

 

Tough to diagnose, so many possibilities. What is really wierd is the single knock description though. Anything that I can think of would knock or slap for a few seconds at a minimum, such as pistons.