525i exhaust rattle

[Twistytee]

I’m assuming the answer is “yes”, but are the exhaust gaskets from the dual pipes to the catalytic downpipes one time use? I dropped my exhaust awhile back to replace my parking brake cables. Re-used those gaskets and all was fine for several months, but now I’ve developed a loud metallic rattle between 1,000-1,200 rpm. I don’t hear it while idling or under throttle, only when letting off the gas and rpm’s begin to settle down to idle. It’s the sound you get with failing cats but I only have 130k on this car and the cats seem solid (i.e. no noise when I tap on them with a mallet). I’ve checked to verify all my hangers/clamps are tight and all appears solid. Not sure what else could be causing this rattle.

[Ed CT]

Maybe the heat shields over the Cats. Sometimes/eventually the fastening metal rots away and they rattle from being loose.

[Twistytee]

Maybe the heat shields over the Cats. Sometimes/eventually the fastening metal rots away and they rattle from being loose.

thanks for the suggestion. I checked all of the heat shields and torqued down the fasteners. I can’t see where any of them are loose or making contact. I’ve also re-checked all the hangers and they are tight. I don’t have any loss of power or CEL so no adverse impact from Cats or O2 sensors. Only thing I can think to try is new gaskets or possible replace the original studs with bolts and new fasteners. The car has been southern owned most of its life so I was able to get the stud nuts loose without braking them, grant it they were still pretty rusty.

[ross1]

I’m assuming the answer is “yes”, but are the exhaust gaskets from the dual pipes to the catalytic downpipes one time use? I dropped my exhaust awhile back to replace my parking brake cables. Re-used those gaskets and all was fine for several months, but now I’ve developed a loud metallic rattle between 1,000-1,200 rpm. I don’t hear it while idling or under throttle, only when letting off the gas and rpm’s begin to settle down to idle. It’s the sound you get with failing cats but I only have 130k on this car and the cats seem solid (i.e. no noise when I tap on them with a mallet). I’ve checked to verify all my hangers/clamps are tight and all appears solid. Not sure what else could be causing this rattle.

I re-use those flange gaskets all the time. Never a problem. Easy enough to get your hand in there to check for leaks but I doubt that is your issue.
Something loose is resonating at that RPM/frequency. Just keep tapping away until you find it.

[Twistytee]

So still chasing down this noise and decided to have my local Indy put it on a lift and check it out. Good news/bad news. The metallic clanking was the center heat shield laying too close the the balanced weight on the draft shaft near the CSB. Every time the shaft would rotate the weight was striking the heat shield. Bad news is after bending the shield back, I still have the dreaded rear CV noise. My guibo is relatively new so I plan to drop the drive shaft and replace the CV joint and the CSB at the same time. Cost of these parts has gone up considerably over the last few years. Is Meyle OK or should I stick to OE BMW for both CSB and rear CV joint?

[KeysCoupe]

So still chasing down this noise and decided to have my local Indy put it on a lift and check it out. Good news/bad news. The metallic clanking was the center heat shield laying too close the the balanced weight on the draft shaft near the CSB. Every time the shaft would rotate the weight was striking the heat shield. Bad news is after bending the shield back, I still have the dreaded rear CV noise. My guibo is relatively new so I plan to drop the drive shaft and replace the CV joint and the CSB at the same time. Cost of these parts has gone up considerably over the last few years. Is Meyle OK or should I stick to OE BMW for both CSB and rear CV joint?

I’m pretty sure my wagon was as cheap as it was because of that same noise. The guy chased that metallic “ring” sound and gave up on finding the source (the driveshaft).
-Donny