I've got 60k on my 2001 QX4, and this is the 1st that I have just noticed a noise sounding like it's coming from underneath the vehicle. It's almost like a rattle but it does not do it all the time. It seems to do it after letting off the gas or when really slowing down. It's not an interior rattle. It's almost like the exhaust is rattling sometimes. but when i checked that, it shook slighty but i don't think it was loose enough to be the source of the rattle. It's starting to worry me a little bit because i can't really tell if it's a rattle or a knocking...?does anyone have any ideas, or have heard a similar sound?thanks for any help

Did you check your shield? They do come loose from time to time.

I'm almost positive I know what this is. It is your rear differential. I have a 2001 with only 45k on it. I was lucky, mine was under warrantly. Take it to an Infiniti dealer and have them check out the rear differential. You might also want to see if it is leaking... it is towards the back of the vehicle.

What you described is exactly what mine was doing. Hope this helps!

thanks for both of these answers. The weather has not been great here so i have not been able to get under the car yet. But when i do I am going to check the sheild and make sure the rear differential is not leaking or low.(by the way, if you don't mind me asking, what was involved in repairing yours?)

Also, before i saw these responses I asked another guy i knew outside of the board, he was convinced that it was the catalytic converter. Do you guys have any thought about this, or do you have any ideas on how i can test myself to see if it's the converter or the differential. Also if it was the differential, wouldn't i hear the noise more often??

thanks!

You wouldn't necessarily hear the differential all the time. The way you described it in your first post reminded me of my issue. It happens sometimes when slowing down or when turning or coming out of turn... at slow speeds. It also sounds like it is coming from more towards the rear of the vehicle. I don't know if your differential will be leaking or not, but I would still have a place check it. Mine was under warranty, so they just replaced the whole differential.

Hope this helps!

thanks for the additional info. I checked my differential fluid level, and it was good. Nothing appears to be leaking. The noise doesn't seem to happen while turning but there is a definite simlarity with our noises at slow speeds. Maybe I just can't hear it at high speeds(but I don't think that's the case)

Did you get any other details other than the fact that they replaced your differential?I've also been reading that it could be a heat sheild making the noise that I am hearing.

what rpm does it rattle at. my 04 pathy rattles at 1600 rpms all the time. it's the exhaust heat shield on the passenger side. The dealer has replaced it like 3 times and it's still there. I'm probably just gonna yank them off one of these but I'm just too lazy.