2004 Nissan Maxima RATTLING NOISE from ENGINE

Check engine mount or exhaust mount/damage

that would be the engine front , you sure it's a Rattle ? if so ? it will be your Camshaft bearing noise, is it a 2.5 L 4 cylinders ?or 3.5 L V 6 !! .
if it's 2.5 L , your Camshaft bearings are starving for oil , so I suggest you check them both intake and exhaust cams and see also if the valve lifters or cam bearings are in bad shape , worn out ? check also both cams journals and drive journals to lifters ( contact operation ) if there is a suspicious gaps between them that also can cause a rattle sound .

No that will not work and it can burn out the engine crankshaft and rod bearings. Use no heavier than 10W30W. I have seen this happen 1st hand.

so many possiable things that could cause a rattle it impossiable to tell you what it is without looking at it
most repair shops will take a quick look at it and tell u what the problem is for free

The first thing to check on a rattling noise is if going over minor bumps in the road if that is when it makes noise is a sway bar link, they make a rattling noise. If you raise that wheel up you might also want to try and wobble the wheel to be sure it is not a tie rod end or ball joint. Typically I run into the sway bar links or the sway bar bushings making the noise. However ive even seen it be a rock sitting on the strut plate.

Maybe its your engine mount that is loose. Try that and let me know if its that.

Your getting backfires? hmm interesting. Seems like your engine is getting flooded and either purging it out of the exhaust or burning it all at once or both (backfire). Sounds like a leaky engine valve to me.There again the bluish smoke indicates to me thatyou are leaking oil somewhere- bad rings or head gasket maybe, which could cause a loss of compression which could also cause your problems.That rattling from the left/rear side sounds like a bad muffler try kicking the muffler (not hard though) next time you walk by it.

This only happens when the Car is Cold???? It is the Exhaust Manifold. You need to Replace the Exhaust Manifold Gasket and check the Rest for Tightness.

I had rattling noises as well (over bumps and when I reved the engine) and it turned out to be the heat shields under the car. I took out 2 heat shields covering the two cats on both sides AND two rusted out dangling rings hanging from the exhaust coupler (have NO clue what they were for)..This has TOTALLY gotten rid of the rattling noise. Good luck!

I have the same issue with my 2004 maxima.The service techs said it was the timing chain tensioners .Since they are hydaulic and they powered by the oil in the car .It is recommended to purge the the engine every time the noise starts to come back. I brought some an it really freaking work because I started to run it into a tree and go buy a toyota