Noise on Acceleration

  1. My model of MX-5 is: 2007 MK3 1.8l
  2. I’m based near: Cheshire
  3. I’m looking for technical help or recommendations on: Noisey Acceleration

I have been working on my car since purchase and had it serviced and they found no major issues, just a bit of rust which needs sorting before the next MOT.

My issue is that when the car is stationary and I press the accelerator the car sounds great. But when driving and I floor it at 4000rpm I get a tin like sound which appears to be coming from the rear of the car. When the windows and/or roof are down I do not hear it. I think the noise could be coming up the drain holes perhaps so I can hear it more when roof and windows are up.

I am wondering if it is the exhaust system, I am looking to get a Cobalt or Cobra or custom one fitted shortly so if it is I am not fussed. It happens at above the 4000 and continues until the revs drop below that threshold.

I have a video of the noise but no idea how to put it in the post. Happy to text or whatsapp to anyone who think they may be able to help.

Any one have any suggestions please?

I get a vibrating type noise when accelerating hard, roof up. I would guess after reading many posts about noise that it could be coming from that shelf behind the seats. That part the hood folds down on to. The hood folded touches it and the vibrations stop, hench when up you can hear the noise hood up.
Not saying it’s your problem but do look at stuff like heat shield above the back box, is it loose, tools not rattling in the cubby in boot. Lastly you can check if the hood drain flaps are in place, a job which needs you or someone to crawl under the rear of the car to check, they can be seen just.
I guess it can’t be anything that rotates, ie bearings or maybe brake related or you’d hear it constantly.

A lot of rattles/buzzing noises at certain revs can be exhaust heat shields, the older a car gets, the more rusty these get and they lose integrity. You can try tapping them and see if they buz or rattle. It’s pretty common on mk1 & 2’s around the cats for example.

Yes the almost common downpipe heat shield rattle on the Mk1. I had fit clamps to mine to stop the rattle. Also I had another rattle up front on the Mk1, turned out it was the bonnet, adjusted the catch.

If I can sort this rattle/noise, I will be well pleased with the car. All the jobs done then I needed to do on it. Got a mate coming over tomorrow to have a look at it - social distancing and all :slight_smile:

Is it above 4000 RPM in any gear or is it gear specific?

Any gear Ian, happens with all of them. Well 2nd, 3rd and 4th anyway. Not tried 5th.

I have known my exhaust to get raspy when flooring it in the wrong gear.
Hope you are able to track this noise down!

Cheers mate

Well I think we have found the noise. Upon acceleration it happens at 4000rpm and also when out of gear as well. When the car was stationary it was making the same rattle at 4000rpm as well. Knocking the cat made a big rattle. So we believe it is the cat which is breaking down. I was going to get a cat back cobalt or cobra, but it looks like my money needs to go on a cat now first. Expensive item it seems to be. Next job is to get it on a ramp just to check it is not a loose bolt or bush etc, but definately banging the cat made the noise. If the cat has broken down, can I get a cat and exhaust from Cobra or Cobalt which will still pass the MOT? Any links please?

Another issues sorted.

Took it to a garage today, showed them the problem, on the ramp and the heat shield had come away from the exhaust near the cat. A new clamp on it and bingo noise resolved. The car now only has the weld issue for the summer for say £300 and it is done ready to put on my own “make it my own car” bits. DELIGHTED TODAY.