First post, hello all

I am experiencing an rattle noise, but ONLY in certain situations.
Please help me get an idea what it could be.

2006 Infiniti G35 Rev-Up all stock 6MT. 134k.

At idle, neutral, Cold. normal noises, runs beautifully.
At idle, neutral, up to Temp, rattle noise SOMETIMES.

At idle, neutral, Cold, A/C on. normal noises.
At idle, neutral, up to Temp, A/C on, rattle noise SOMETIMES.

Driving, under load, any gear, between 1k-2k RPM, rattle ALL the time, with or without A/C on.
Driving, under load, any gear, after 2k, normal noises.

Driving, in gear, throttle off, no noises, any rpm.

I had one mechanic tell me, "its your A/C pulley", but with the A/C on or off, same noise in those situations.
Online posts/threads say could be Timing Chain, but doesn't the timing chain rattle under load after 2k RPM? This only rattles in between 1-2k, and only under load, not at idle (sometimes). My engine braking makes no rattle, I heard others does when timing chain related.
I personally am thinking exhaust heat shield? But I have not gone underneath to look (no jack)
Some online posts say "throw out bearing", but I just had my cars Slave and Master clutch cylinder replaced, with no change at all to the noises, and the transmission shop (reputable) says clutch, transmission, etc, are in great shape.

It is driving me nuts... Anybody experience these symptoms, to kind of give me an idea where to look/fix?

Thanks!

 

AC pulley is spinning regardless of the AC being on/off. It's driven off the crank pulley and when you hit the AC button it causes a clutch on the front of the AC compressor to magnetically pull up to the internal shaft to drive the compressor. The idler/tensioner pulley and the AC compressor pulley are spinning with the engine.

The idler/tensioner pulley that the mechanic was talking about is a known wear item on all cars, you diagnose noise the pulley by removing the AC drive belt and spinning the pulley by hand, it should have zero noise and barely make one full revolution when you spin it by hand.

However it almost never makes an intermittent rattling noise, a bearing noise is unmistakable, sort of a whirring/hissing sort of sound. This video at the timestamp is what an idler/tensioner sounds like when they go bad.


Timing chain rattle can make that sort of noise but on the VQ it will typically start making it's noise on a cold start immediately after the engine fires and will rattle for about 1 full second while the engine builds up oil pressure to push on the tensioner (it's driven by oil pressure). There are components in the timing assembly that can rattle but they're almost never an arrhythmic type of rattle, usually it's very easily reproduced at certain engine rpms. This meets the criteria of the noise you described so yes you might need a new timing chain tensioner. It's a fairly simple replacement that takes about 30 minutes and the OEM tensioner costs roughly $75. Nissan part number 13070-EY00A

Clutch throw out bearing only spins when you touch the clutch pedal, what you are doing is pushing the TO bearing up against the release fingers on the pressure plate. With the clutch pedal released the TO bearing is floating and not spinning. When they fail it is ALWAYS a noise associated with pushing in the clutch pedal and it makes a sound very similar to the belt idler/tensioner pulley in that video I linked.

The heat shields on the cats can also make a rattle that is related to specific rpm and load conditions. And to make matters more complicated the element INSIDE the cats can also make a distinct rattling sound. I have a set of used test pipes that I picked up specifically for diagnosing whether the rattle is cats related or not. If you're paying shop labor to have them installed it's not a very good troubleshooting recommendation but if you are installing them yourself you can pick up a cheap used set for well under $100. The cat heat shields are highly notorious for rattling. I welded the sides, front, and back of mine in a half dozen places almost immediately after I bought my car.

If you were not installing them yourself another inexpensive/free way to test for the cat rattle is to simply remove the shifter console, the boot, and the rubber dust boot so you can look down at the top of the transmission then just go for a drive. The cats are very close to that opening and you will easily hear the sound. It is possible to leave the console attached and just rotate it 90 degrees, then lift up the dust boot. Unscrewing the shift **** can be a pain, just be aware that there is a lot of impingement on the shifter when doing this so you might have trouble trying to find the right gear.

 

Thank you for your reply!! I will loot into ALL of these potential fixes

It is for sure coming from the back of the engine (thank God!!)

I have a video too, I recorded after it was all warmed up.. Maybe you or someone can know just by hearing it :/


Thanks again!!

 

Maybe look into your Exhaust Bolts just in case as well, when I did a flexplate change, I forgot to bolt those down and it made my cars exhaust sound worst and a rattle towards the bottom of the car, did you do any exhaust work on that? It sounds close to what mine did when I didn’t bolt down the exhaust bolts... On a scenario that could be worse, it could be a loose torque converter bolt but that’s very situational and highly unlikely…