The car is an MX5 NC Roadster 1.8 Venture edition, 2012.
The problem is noise that seems to be coming from the rear end, which I would love to diagnose and fix. I appreciate that it is not easy to identify a noise under the car that can only be heard while you’re driving it however, here goes.
Noise can be heard only above about 20MPH. It’s high pitched - a cross between a whirring and a rasp. It sounds metallic. It’s not a rumble or a whine (wheel bearing or diff). It increases in volume as road speed, not engine speed increases. There’s no difference while accelerating, coasting or on overrun. It’s intrusive at speeds above 50mph.
Can’t hear the sound when the car is run with rear wheels off the ground.
First thoughts were that it was tyre-related. Swapped tyres with another MX. No difference to the sound.
2nd impression was that it was coming from rear/left side. Wheel bearing replaced. No difference to the sound
Next consideration given to diff. Oil drained. What came out looked good. Oil replaced. No difference to the sound.
Transmission professional brought in who thought that it was a diff problem. Diff removed and opened. Concluded that pinion bearing/s worn. Replaced these. No difference.
Don’t know where to go from here. Anyone got any ideas?
Just a thought, but It’s possible this is just road noise coming up through the drain holes behind the seats, there are various ways to block the bottom of the drain holes to help dumb down the noise , but still allow you to rod the holes out to keep them clear with a Trombone cleaning wire, its usually worse with the lid up, I hear all manner of creaks and noises, but have got used to it , it seems to be a characteristic of soft top sports cars, or maybe its just me !
As it is speed related, could it be something vibrating in the wind? Any loose panels, or even worn rubbers allowing the exhaust to touch something? My immediate thought was a loose heat shield, of the rear bumper ‘flapping’ in the wind.
I’ll go with drain hole noise the same as Boz.
Never given it a thought, you say Roadster are the drains the same as the soft top people? If so you could try as Boz says and temporarily stuff the bottom outlet up with foam then go for a drive. Also the drains can become dislodged thus creating the road noise.
Others have stuffed some filter foam in there, the type used for fish tanks.
Worth looking at to eliminate this noise.
I can only hear mine when the roof is up.
I was convinced that it was a wheel bearing on it’s way out, until i noticed that it changed pitch on different road surfaces.
General concensus is that it’s the drain tubes, allowing road noise, I do intend putting a bit of foam in the ends to prove the theory, but just havn’t gotten around to it.
I had exactly the same speed related noise on my 2010 soft top when the roof was up.
Luckily I had just purchased the car from my local Mazda dealership and they fitted two new drain tubes (both tubes had the flaps stuck open) under warranty, as soon as the new drain tubes were fitted the noise was gone.
If the car had not been under warranty I would have tried the filter foam fix.
Many thanks to all who sent suggestions. The noise was coming up through the drains. Problem now sorted by getting bottom flaps back where they should have been. Sound insulation also added to seat belt anchor cavities and panelling behind the seats. I’m surprised but also very pleased to find the solution. Thanks again for help.
