Has anybody heard a knocking sound during idle that happens about every 10 secs coming from the exhaust/catalitic converter area?

Was sitting in my GP the other day and heard this sound -- almost like someone underneath was hitting it w/ a hammer. I'm new to the car and am not sure if it is normal or not. Asked the prev owner and he wasn't aware of it.

Loving the car otherwise.

Thanks for any thoughts.

 

You mean the crackle, pop, burble? If I think thats what you're talking about then its normal. Happens when you let off the gas too.

I wish the 2010 MCS did it too. Its a cool sound. I REALLY WISH my M5 did it also. I can only imagine how freaking crazy that would sound.

 

It might me the exhaust hitting somewhere under the car. Try grabbing the exhaust (when cool) and shaking it to see if you can duplicate the noise. I would try shaking from the middle and the back of the exhaust to determine if one of the rear or middle hangers is weak or broken. I would not be surprised if the middle hanger is weak.
http://www.waymotorworks.com/r52-r53...ger-mount.html

 

This is definitely not what I'm referring to. I love this sound too when letting up on the accelerator. I wish it just was that.

This sound happens once every 10-15 seconds and its a loud bang sound--almost as if heat is expanding and/or cooling around metal. Kind of like taking a cookie sheet out of the oven--or into the oven!! It's not a vibrating sound or a sound that is constant.

It's got to be the CAT cooling down from being hot? As metal cools, it contracts--kind of like that sound. I'll have to listen/describe it better. . and I will check the exhaust hangers in the meantime--thanks!!

 

I think your car definitely needs a German tune up after sitting around for 5 yrs. I highly recommend you take her out and put her through the ringer. At least 5-10 hard redline shifts should clean her out! hahahaha

I give all my cars German tune ups at least once a week! No issues so far