I have been trying to isolate a noise in my 2002 Infiniti I35 (I believe the some Maximas share the VQ35DE engine). It doesn't occur when I'm heavy on the throttle, just when I gently apply power and at about 25-45 MPH a small rattle/ tinkle noise comes from the engine. I have tried different fuel grades and brands to see if the engine is predenonating. I also performed an induction cleaning. The noise seems to be aggravated by temperature as it is more pronounced in the Summer (110 degF), and faint in the Winter (65 degF).
The FSM suggest that it could be a timing chain tensioner, and I have been told it could be a heat shield, but the heat shields on my exhaust don't seem loose.
All three motor mounts in addition to the transmission mounts are brand new. The oil level is good, and has been changed at about every 3500k. The car has ~138k on the odo.
Does anyone have any suggestions? Old spark plugs?

 

It can be pinging sound or spark knock. Need to replace sparkplug, check ignition coil, its better to change the rear valve cover and gasket use the 6th gen (2004 valve cover gasket. I recommend to install a pcv oil catcher to minimize the blowby oil contaminating the intake manifold. The VQ35DE is known for this because it has a tapered piston.

 

If you get the sound as the RPMs drop when you rev the engine while parked, I found it was caused by the bank 1 pre-cat. Sadly if this is the case it means the engine likely sucked in catalyst material and as a result will start to burn oil.

If not, then you get the sound at light throttle because the timing chain tensioner isn't fully keeping the chain tension free. There is a youtube video of the vq35 timing chain tensioner which can help illustrate this.

 

Could be tensioners, I would start by running 2-3 tanks of premium to see if that solves the issue. Most likely ping.

 

Failing MAF.

 

I had a similar issue with my girl friends car. It sounded like a marble inside of a paint can. So I was doing the catalytic converters last weekend, and when I dropped the front pipe, there was a piece of metal inside of the heat shield that was causing the rattling. The piece of metal came from broken bracket.

 

This is most likely the cause if it's not pinging (93 octane should fix that or remove it to a min). It's another common problem. POS heat shields rust away. I've seen them completely fall off on the highway

 

Mine does both haha. Makes noise when RPM drops and Accelerating at 2k RPM mostly in 2nd gear. I burn about a quart every 4000 miles.

My question is, if I gut the precats and get the timing tensioner replaced will it eliminate or at least reduce the noise??

 

Yeah, the front one will rattle when the cats are shot. At that point your engine is getting ****ed up.

Yes, gut the cats. Before it's too late.

 

When the idler pulley bearings go it makes a really similar noise just changed mine sounds great now