Miata Mailing List: January 1993, Message #69
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   From: (none)
Subject: Exhaust Noise and Exhause Tone
   Date: (none)

Has anyone noticed an increase in exhaust sound with a change in the
catalytic converter or with the replacment of the old muffler for a
new one.  My catalytic converter was changed as a result of the Mazda
recall.  The car then sounded very noisy and boomy. The dealer decided 
that the problem was with the muffler.  I told him that it wasn't the
problem but it was changed anyway.  The new muffler had a much lower
pitch exhaust note than the original (1990 Miata) and the booming
problem got even worse.  The dealer then found that the problem was in
the heat shield of the new converter and replaced it again with a new
one.  This helped the problem but did not eliminate the booming sound. 
The mechanic who worked on the car told me that it was his impression
that all Miata's that had their converters changed bercame louder and
that the new converters were probably of a different design.  I am not
sure that I believe that since a 1992 ot 1993 Miata does not have
any increase in sound. Its possible that the increase booming noise is
due to the new muffler which has a decided lower pitch than the
original.  I remember reading in Miata Magazine a letter from someone
who stated that they had a new muffler replaced under warantee which
had a very low pitch exhaust note and they were unhappy with the
replacement.

Enough rambling with my story.  I would like to know if anyone has
noticed an increase in exhaust noise with the new catalytic converter
since I think that the Dealer may be giving me a story and I will push
Mazda to replace the converter again.  Also, has anyone noted that
recent replacement mufflers have a different sound or pitch which
could be responsible for the booming sound.  The increased noise is
not due to problems with brackets or heat shields since they have been
checked.

Thanks for your help.

Herb Samuels