Apologies if this has come up loads of times before, but at my last service they said the cat heat shield is corroded. That was about 5000 miles ago and just recently there's been an awful resonating noise just over 2600 revs. Could this be the cat heat shield and, if so, is anything sinister about to happen to anything or can I ignore it (which is difficult, it's so loud) until the next service? Has anyone tried a self fix for a loose CHS? (3/00)

I get a similar resonating noise at about 3600 rpm. To get rid of it I removed my Cat shield, but it wasnt that. I think its actually the manifold heat sheild in (look at the engine, where the zorst attaches to the right hand side as you look under the bonnet) Bit of alloy with a dont touch symbol (this is the manifold heat shield). Im thinking of removing this to see if this gets rid of the noise.

If I were you I'd get someone to stand near the car and then see if you can determine between the two of you where the noise is coming from. I know people who have binned both sheilds without harm. (3/00)
Any rattling noise (underneath) is likely to be a heat shield. My cat heat shield did the same 18 months ago. Took it to a tyre place on spec & they did a quick braising / solder job for a fiver. It's still fine. (3/00)
I had a bad resonant vibration when I accelerated gently from 40 mph in 4th gear. I was told that the two hood drain pipes that run either side of the rear axle and come out just in front of the rear wheels vibrate during acceleration and this caused the exact same sort of noise that you describe. My dealership did a modification under warranty which has completely cured the problem. If you look under the car you can see these pipes. (3/00)

Is this a metallic vibra-noise? I get one from 2600 to 3000 revs which really annoys me. It started a few days ago. I thought it was at the back box of the zorst (to coin a phrase), but on saturday I was fiddling with a (I'm sooo technical) 'thin heat-shield-like tinny cover' at the bottom of the downpipes, after a technical diagnosis with head hanging out of driver's, door neck on sill, blipping the throttle.

It's not the manifold heat shield with don't touch symbol, but appears to be another little shield where the pipes meet the exhaust. It seemed to stop the noise for a while...It started up again after about 20 miles. Maybe I didn't lever the metal cover away from the pipes far enough....I have been considering wrapping something around it to hold it tight. (3/00)
I keep reading about the removal of damaged heat shields. Am I the only one who thinks Mazda would never fit expensive bits like this if they didn't have a fairly critical purpose? I can't see it's climate related, as exhausts get just as hot whether you're in Texas or Barnsley. Any opinions? (Does anyone get very warm feet without the heat shields? ;-) ) (3/00)
I thought the heat sheild was just there to stop you burning your hands on the very hot manifold and to tidy up the look of the engine. (3/00)

Don't get confused, here, folks. There are at least 3 heat shields.

1) On the exhaust manifold. That's the one I don't have (re Simon) 'cos I've got a non-standard manifold and it doesn't fit (and was thrown away long before I got the car). That one does stop you burning your fingers (or at least instantly charring them), it tidies up the engine compartment and it reduces underbonnet temperatures near your air intake. My manifold is wrapped in special heat-wrapping (see Demon Tweeks) to reduce temperatures (even though I have my own design CAI).

2)The cat heat shield. Located, surprisingly enough, just above the cat - that's about by the handbrake lever. I've still got mine - it's in surprisingly good nick, and I imagine without it the transmission tunnel by the handbrake would get even hotter than it does anyway. It is well worthwhile taking steps to reduce temperatures of the tunnel - make sure the intermediate gear shift boot (the rubber one under the leather one) is intact, and the base of it is flat and contacting the tunnel all round (it tends to get rucked up). Demon Tweeks sell expensive heat insulation sheet - it's a good idea to line as much of the tunnel as you can get at with it - it goes under the carpet, shiny side to the metal. Concentrate on the left, where the exhaust pipe is - that's where most tunnel heat comes from. Summer is coming! :-)

3)The silencer heat shield - under the boot floor, and just above the main silencer. Likewise, without it, I reckon you could leave a chicken to slow roast in the boot. So - none of them are vital, and all of them can vibrate if they corrode or a bolt comes loose, but civilised sports cars are not supposed to roast you any more (ah! for the Austin-Healey 3000 ;-) ) (3/00)
I noticed the rear exhaust heat shield last week for the first time while polishing the exhaust tip. Mine looks to be in a bad way although it may just be dirt. I get an annoying buz at about 3000 revs, the Mazda dealer put a jubilee clip on the cat heat shield to stop this buzzing. Any idea what else could be causing this ? Have to get the rust killer out and have a go at the rear heat shield I guess to. (3/00)
Ah yes - there are more shields on the cat itself (rather than fixed to the body) and on the exhaust pipe behind the cat (on some cars). These can start to detach themselves from their fixings and start to rattle or "ziss" - you can generally fix these with a jubilee clip - for a while at least. Sometimes things become detached inside the cat or silencers - you can't really do anything about them except fit new components. Finding things which vibrate at particular speeds/revs can be very frustrating! (3/00)

My manifold is wrapped in special heat-wrapping (see Demon Tweeks) to reduce temperatures (even though I have my own design CAI).

.. bad feedback about wrapping manifolds on miata.power .. they could not take the heat and 'burnt out' .. I guess accelerated corrosion due to elevated temps .. just a warning. (3/00)

Here are at least 3 heat shields.

Four. In addition to the three mentioned above there is a fourth one on the stock exhaust. It is fitted to the exhaust (not the car) where it goes under the back axle. It is held on with three clips. If you have changed your exhaust you probably don't have this one. One half of this heat shield started vibrating last year on my car. Before I found out it was the problem it fell off. I have had no ill effects yet.

Like others say, I think Mazda put them on for a reason. However I don't know what the reason is yet because there seem to be an awful lot of MX-5s running about with missing heat shields and no problems yet. (3/00)