Miata Mailing List: March 1995, Message #122
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   From: "Drake A. Daum" 
Subject: 3500 RPM Rattle
   Date: Thu, 2 Mar 1995 15:31:30 -0500

     To Jyri, et. al.:
     
     This topic seems to keep popping up over time (OK, class, once 
     again...) 
     
     You have just experienced the classic exhaust pipe heat shield rattle.
     
     Immediately downstream from the oxygen sensor is a small clam shell 
     heat shield welded to the exhaust pipe at one end.
     
     Over time, this small spot weld fatigues and breaks.  Then the sheet 
     metal shield rattles freely against the pipe.  Resonance takes place 
     approx 3500 rpm.
     
     Mazda has issued a Service Bulletin to all their dealers to fix/repair 
     for free.  
     
     Personally, I just ripped the sucker off the pipe and threw it away -- 
     no more rattle.  I didn't want the exhaust pipe and manifold disturbed 
     by the dealer.
     
     If you want this small shield to stay on the car, ask your dealer 
     service dept. to check the Miata service bulletins for the one on 
     exhaust rattles.  Don't confuse this with the service bulletin on 
     catalytic converter rattles caused by the failure of the pinch flange 
     around the perimeter of the cat.  This is entirely different problem 
     and is covered by another dedicated service bulletin.
     
     I have copies of these two service bulletins in our club files, but I 
     don't recall the exact numbers and issue dates by memory.
     
     Cheers,
     DRAKE A. DAUM President 
     Miami Valley Miata Club
     PO Box 33503
     Dayton, Ohio 45433-0503