Hello I have a 2008 G35Xs with 111,000 miles and I've been getting this weird sound coming from underneath the car while idling and coasting. This sound reminds me of a tumbling ball or a percolating like sound. I had the car on the lift a about two months ago and I checked the heat shields for rust and corrosion. I didn't see anything obvious, plus it was tough to tell where the sound was coming from. I almost thought one of the cat cores was broken up and was causing this noise.

Anybody else have this problem?

Dave

 

So I got my car up on a lift today and the cat heat shields were worse off than I thought. I removed them pretty easily with some pliers and large screw driver. After removing the shields I started the car and the noise was still there. However it was easier to pinpoint where the noise was coming from. Seems the drivers side cat core has come loose and is tumbling around inside.

So I'm thinking of replacing the stock cats with some aftermarket high flow ones. Only problem is the cats have three bolts that mount directly to the exhaust manifold. Two of the bolt are easy to get to, but the third is up out of the way. Might have to lower the engine to gain access. Also they are rusted up pretty good.

Anyone have any problem removing their cats?

 

Anyone here successfully remove the cat?

 

Take day one to put penetrating oil on the connections and bolts and the next day town all the bolts off.

 

I got a same thing going on with my coupe. It's your cats. I think the reason why my failed is due to all the oil that is being eaten up by engine. I'm not getting any codes, but I do get the rumble from the cats. I'm sure that it's the element inside that has failed and just rumbles around inside.

The one difficult bolt you talking about is accessible from the engine bay with an army of extensions. There are threads and videos on DIY cat installs. Just search for them.

 

Thanks for the info Joker. I'm going to swap out that cat in a week or two.

 

+1 for the army of Extension