Noisy rear end under load at low rpm

IanR · Postby **IanR** » Sat Mar 03, 2018 2:18 pm

Hey,

Hoping someone has had a similar issue.

Since I have owned this 98nb (3.9t2 diff and 6sp gb) it makes a metallic vibration/grinding noise from the rear in any gear under light load or heavier from about 1500 to 2000rpm. As soon as I hit 2k the noise is gone.

I can drive with very light throttle though this range and no noise but anything more than light and it rattles/vibrates/grinds.

Had a diff guy in the car driving it and thought a loose something but wasn't thinking diff as it sounded a dry noise and not a wet noise as he put it, relating to in oil. I have not found anything loose.

Any idea?

Cheers
Ian

The American · Postby **The American** » Sat Mar 03, 2018 2:31 pm

Sounds like a heat shield issue, or the exhaust contacting the rear subframe somewhere

jordan.k · Postby **jordan.k** » Sat Mar 03, 2018 2:50 pm

This won't really help but my car makes the same noise vibration/noise under load at that rpm.

I wouldn't worry about it too much as I've done thousands of kms with it and had a few different diffs in there with all the same noise. I've heard somewhere it may have something to do with ppf alignment but I am not sure.

I rarely find myself at that rpm anyway so it doesn't bother me

Postby **NitroDann** » Sat Mar 03, 2018 4:22 pm

Absolutely TONNES of mx5s make the 1000-2000 rattle. Ive never bothered to investigate particularly hard but I think its around the centre of the car not the rear.

But yes, tonnes and tonnes of MX5's do it. Most 1.6s do it and I see it on NB's often enough also.

Dann

IanR · Postby **IanR** » Sat Mar 03, 2018 5:45 pm

Thanks, I’ve got some new end links to fit on the sway bars so will see what I can find again. I’m not too worried by the noise just like the car to be quiet and sound smooth. Thanks for the inputs

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IanR · Postby **IanR** » Sun Mar 04, 2018 5:54 pm

NitroDann wrote:Absolutely TONNES of mx5s make the 1000-2000 rattle. Ive never bothered to investigate particularly hard but I think its around the centre of the car not the rear.

But yes, tonnes and tonnes of MX5's do it. Most 1.6s do it and I see it on NB's often enough also.

Dann

The more I zearch I can see it is very common, the silver NB was a rare and special car that made no rattles... :wink:

StuwieP · Postby **StuwieP** » Sun Mar 04, 2018 9:45 pm

I think I've got exactly the same thing too.

Does it feel like there's a bit of slack in the driveline?

Place I bought it from had replaced the diff and I wonder if they didn't get it all back in straight. Since nothing's stopped working in the 5 years I've had it I haven't bothered to spend $$ on trying to troubleshoot.

Can confirm though if you keep it at 4k+ all the way to redline and back, there's no such sound.

IanR · Postby **IanR** » Mon Mar 05, 2018 7:28 pm

StuwieP wrote:Can confirm though if you keep it at 4k+ all the way to redline and back, there's no such sound.

There is no vibration/grind if the rpm is over 2k or light load under 2l, the worst scenario is say when rolling through a corner and loading up the motor at under 2k, just happens every now and then toodling around town. Even taking off at the lights say is fine for some reason....

Postby **NitroDann** » Mon Mar 05, 2018 7:34 pm

Thats a pretty accurate description of what i have experienced.

Dann

IanR · Postby **IanR** » Mon Mar 05, 2018 7:37 pm

NitroDann wrote:Thats a pretty accurate description of what i have experienced.Dann

...are you tying to suggest that we agree on something?

Postby **NitroDann** » Mon Mar 05, 2018 8:00 pm

With out any shadow of a doubt.

Dann

StuwieP · Postby **StuwieP** » Mon Mar 05, 2018 9:04 pm

yep.

well, if anyone finds out what it is... let us know. Or if I do... vice versa.

greenltd · Postby **greenltd** » Tue Mar 06, 2018 10:07 am

Could be a different noise, but i sometimes get a vibration noise from the boot lid springs so maybe have a look at them. Had me stumped for ages. I get it sometimes when stationary as well.

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IanR · Postby **IanR** » Wed Mar 07, 2018 11:04 am

Thanks greenltd yes this one is an engine speed/load related vibration that is definitely gearbox or rear end.

It can be created by quick kicks of throttle as well when coasting, a metallic grind as the load goes from the box.

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ManiacLachy · Postby **ManiacLachy** » Thu Mar 08, 2018 1:53 pm

My car used to have the low RPM rattle as described, I'm not 100% sure when it happened but it's no longer there! This thread has only just made me realise it. :mrgreen:

I suspect it was when I installed the polyurethane differential bushings. Whether it was the new bushings that fixed it, something going back together better than it was beforehand, or some part I left out, or something else along the way, the noise is gone now!