NA 'drones' with roof up

oilman · Postby **oilman** » Sat Mar 25, 2023 12:09 pm

I have an NA Limited Edition that has done 135k. I bought it about 6 years ago and I have only done 5K in that time (usually short runs on good days with the top down). I have just returned from a 4 day trip where I did 1100km. I nearly turned around and went home after about 50km as the droning like sound at 100km/h on the freeway nearly sent me around the twist. It sounds a bit like a diff problem, but I have been assured by an MX-5 specialist there are no issues and the sound doesn't change whether you accelerate, back off or coast in neutral. I don't really feel any vibration. I pulled over, put the roof down and did the rest of the trip that way (with the heater on) and the sound mostly disappears (but sometimes I do need to be able to drive with the roof up!). To be honest it has been the same since I bought it, as I noticed it when I drove the car home. It has a standard exhaust. I put it up on my hoist and ran it up to 100km/h and the only thing I noticed was a vibration around 70km/h. Wheels aren't damaged. Any ideas on where to start? I was going to get the wheels balanced in case it was something simple.

KevGoat · Postby **KevGoat** » Sat Mar 25, 2023 3:06 pm

Diff, gearbox, wheel bearing, tyres, fuel pump, the lack of any sort of sound deadener in these means every noise comes through. Mine (SE) also has a NitroDann exhaust. Top down, these are hardly noticeable apart from being able to hear the exhaust note better (a good thing), but soft top up, and all these become more noticeable. Hardtop on, and it's almost unbearable at certain speeds. I did recently find some leaks in the exhaust from loosened manifold and joint bolts that I've fixed, and this has made a huge difference to the droning. I get a whine from the diff (I assume) that used to concern me, that I've since been told it is quite normal.

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93_Clubman · Postby **93_Clubman** » Sat Mar 25, 2023 5:32 pm

oilman wrote:NA Limited Edition that has done 135k - bought it about 6 years ago and have only done 5K in that time - droning like sound at 100km/h on the freeway - sounds a bit like a diff problem - been assured by an MX-5 specialist there are no issues and the sound doesn't change whether you accelerate, back off or coast in neutral - put the roof down and the sound mostly disappears - been the same since bought - up on hoist and ran it up to 100km/h and the only thing was a vibration around 70km/h

A number of possibilities but from your explantion it sounds like a soft top issue as it's present when up & absent when down. How old are the tyres according to the manufacture date on the sidewalls? NA6s benefited from adding a rear brace under car as well as a brace across the seatbelt towers like the NA8. My old NA6s rear end was a little noisy depending on the type of road surface. Are you absolutely certain the whole exhaust is standard & do you also mean it's original?

KevGoat · Postby **KevGoat** » Mon Mar 27, 2023 5:32 pm

Just recalled an annoying sound I couldn't solve for ages in another car, though I'd describe it more whining than droning (no, not the passenger!). I eventually found it was the power steering fluid was low. Topped it up and all good.

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