I have a 2003 I35 with 220k miles that has always had the slight timing chain rattle, but it seems to have something new now. I first noticed it while driving it would rattle while coasting, or with barely any pressure on the gas. Under load, it doesn't rattle at all. Then I tried it in park, and it gets very bad (sounds almost like rod knock) about 1300-1500 RPM. If I put it in gear and hold the brake, it doesn't do it at all when giving it gas. It sounds like it's coming from the front right side of the engine (passenger side), so I thought it might be the power valve but that seems fine, it actually sounds a little further in towards the middle of the engine and lower. Because of this, I'm not sure if it's the timing chain as it doesn't really sound like it's from that area. Anyone have any ideas?

 

sounds like broken guide/tensioner
Take off access cover to inspect.

 

My 2003 i35 had the same symptoms at 170,000 miles a couple of years ago. You can get an inexpensive mechanics stethoscope to pin point the source of the rattle sound. My problem turned out to be the broken plastic tensioner. That was my COVID project in 2021. 😩

 

Mine had that. I imagined that it was the idler pulley. It eventually went away after two years. So odd that it just fixed itself.

 

i was going to suggest the same, idler pulley, super classic rattle in that RPM range, i have had the noise for 10 years, i am over worrying about it

 

I had the same noise in my 2003 SE Maxima. My car lost about 1/2 quart of oil every 500 or so miles, I knew it was low on oil by the rattling noise it made when I drove up the hill to my house at the time. I was aware of it possibly being the plastic guide tensioner but that wasn't the case with my car.