Thundertub

No, it's not IMS or anything deadly. It is a metallic rattle that is coming from the rear when the engine is hot for some time. Only occurs when you give it a little gas in the lower gears. Definitely metal.

I'm thinking either a loosening heat shield somewhere, or a cat with a loose plate, or something in the muffler. If the car sits for only a few minutes after being run, the rattle takes time to come back.

Been getting progressively louder and more rattley over the last week. I have had a very competent Porsche tech ride with me and he thinks it is exhaust related, and maybe a cat. I'm hoping cat so I can replace them both with 200 cell units. The current cats are the originals (December 1998 build date).
Also have TechArt exhaust after the cats. That is also same vintage as the original cats (swapped out the stock mufflers at original delivery).

Any other ideas from out there on this rattle?

Pac996

No but I have been tempted to ditch the cats and put glass packs or straight pipes. Probably best to replace the mufflers with glass packs and keep cats.

rotokim

I just had the same problem - it's my drivers side muffler. I'm going to replace both mufflers. My tech said it's b/c I've been driving the car wide-open at the track and the stock OEM muffler isn't designed to handle the pressure. So, I'm getting a set with by-pass pipes from Fister. Can't wait.
Bob

ivangene

get the a$$ of the car in the air when its hot - and knock the exhaust with a mallet here and there... you might issolate the sound that way

LVDell

Now we're talking!

smackboy1

Another possibility is the heat shield from one of the brakes is rubbing against something. This happens to me after a track day so I think it's because the heat causes the metal to change shape. The sound frequency changes with wheel rotational speed. It's usually the heat shield rubbing the rotor so I just bend the metal back at bit.

One way to try to isolate the source of the sound is to stand by the side of the road and have a friend drive your car by you both ways and at different speeds until you figure out where the sound is coming from. If you have no friends I suppose you could drive next to a wall or some other flat solid surface with the windows down and listen.

waynesworld

Mark,

The rattle is likely coming from muffler internals. You can find more details in this post https://rennlist.com/forums/996-foru...al-repair.html

-Wayne

leftlane

I had this happen to my aftermarket exhaust - it was the internals of the muffler as stated by waynesworld.

Barn996

Nice.

911FM

Possibly Catalytic Converters?

FM

redridge

+1 on the mallet.

rotokim

If it turns out that you need mufflers, Darin Fister has been great to work with. He has PMd me promptly with an answer for every question I've had.

Dell and Barn996 - Thanks! I'm listening to sound bites of other modified 996s daily until the parts arrive b/c I'm so excited about it.

Bob