Miata Mailing List: August 1992, Message #38
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   From: (none)
Subject: Exhaust Problems
   Date: (none)

Gordon asks about a nasty exhaust buzz at 3300-3500 rpm.  I had
a similar problem with my car, athough the specific resonance
point was more like 3800-4000.  It turned out that a spot weld
had broken and the heat shielding on the header (probably the
same one you mentioned, Gordon) was vibrating enough to contact
the pipes and make a really ugly noise.  About five minutes on
the lift at a local muffler shop, and the problem was gone.  We
decided to just bend it out of the way rather than rewelding it
since chances are it would just break again.

By the way, in no way can I really blame Mazda for this, since
the day the weld broke, the car had been subjected to some very
enthusiastic driving over the rumble strips at a kart track we
use for autocrossing.  I have no doubt that the weld broke due
to the unusual flexing induced by such adventures (not because
Mazda has any trouble making proper exhaust systems).

Steve Bruun