Hum / Whine

My Miata has been making a noise for a while now. I'd gotten used to it, but my dad pointed it out so now I'm starting to worry a bit.

The car makes a hum/whine noise proportional to road speed. Sounds a lot like tire noise, but I don't think it changes if I change tires. The noise only seems to be affected by road speed. It does not change substantially when under power, cruising, or slowing down (although pitch goes up and down a bit with speed). The noise does not change if I put the car in neutral.

I think the hum is coming from the rear of the car. All this has me thinking it could be one of three things: differential, CV joint, or wheel bearing. The differential is a Torsen that I got used from a Spec Miata guy. It was on a parts car he'd picked up, but from a year with the wrong gearing for his car, so he gave me a good deal. Supposedly it had been put together by a good Spec Miata race shop not too long ago.

This has been ongoing for a while now, and the volume and it has not gotten any louder or changed as far as I can remember. It makes me think it might not be something to worry about unless it actually changes substantially.

The differential seems to be the obvious thing to me. I think I may have slightly over-filled the diff when I put fluid in. I filled it until it started to flow back out, but only the back of the car was raised, not the front, so I probably filled it with more than the correct amount.

Any other thoughts or suggestions?

I dunno man, but I am in the exact same boat with my RX-7 (which is a solid rear axle). I saw some grease weep on the inside of the driver's wheel, so I just did the outer wheels bearing, race, and seal (the bearing was bad) but the noise did not go away. I have RP in the diff filled to a fingertip under the fill hole with no metal shavings or burning smell. Both axles seem fine as do the bearings, nothing gets hot or weird. It's just... noisy.

I'm starting to think it's gear slop as with the driveshaft out you can move the pinion flange back and forth (rotational) quite a bit.

Basically, I don't think it's CV joints or anything like that on your car since a SRA car is doing the same thing.

Can you hold the computer closer to the car? I can't hear it very well.

P71 wrote: I'm starting to think it's gear slop as with the driveshaft out you can move the pinion flange back and forth (rotational) quite a bit.

Actually, that makes a lot of sense. It does seem like there's a bit more drive-line lash than what would be normal. Just judging by how far the car can be pushed back and forth in first, with the engine off.

Seems like that wouldn't be worth worrying about, since the noise isn't getting any worse.

Otherwise, I suspect the fix would be to pull the diff housing and take it to a rear-end shop to have them reset preload and backlash.

Usually if it's gear lash the noise will change from power on to cruise to coast. I would say bearing noise. Possibly a pinion bearing.

Toyman01 wrote: Usually if it's gear lash the noise will change from power on to cruise to coast. I would say bearing noise. Possibly a pinion bearing.

Will pinion bearing noise sound the same as wheel bearing noise? Any suggestions on telling which one it is?

If it is a pinion bearing, how big is the concern? What would be the best way to fix it?

Does the noise change going around a corner?. If so, wheel brng.

iceracer wrote: Does the noise change going around a corner?. If so, wheel brng.

I'll have to check on that one.

Mine didn't change going around a corner :(

It's got to be in the ring & pinion somewhere. Pinion bearing, gear slop, ring gear bearings? It's got 233,666 miles on it...

Pinion bearing noise is generally load sensitive, diff bearings are too but not as much. As noted earlier, wheel bearing noise changes with turns and this is noticeable in lane change manuevers. R&P noise can be load sensitive too, but I have seen 'whiners' which were speed sensitive but never gave a moment's trouble. The Trooper's had a speed sensitive whine (50-65 MPH), it's been doing it ever since I got it 70K miles ago and has shown no ill effects.

Very doubtful it's CV noise. Those don't whine, they rattle.

I did not notice any change going around corners.

It's also not especially loud. I generally can't hear it until above 35mph, because I'm accelerating less aggressively. Otherwise it's easily drowned out by any other noise.

One other thing to chase is does the frequency of the noise change with turns? That helps you locate it.

For example, my 1st RX7 had noisy spyder gears. Very slow rythmic rumbling whine. rrrRRRRrrrrr......rrrrRRRRRrrrrr....

Slight drift to one side would speed up the rate, slight drift to the other side would halt the change.

Why not drain the diff and refill with LUCUS rear diff oil if the noise is less or gone you know you got somthing in there wearing / out of adjustment. The LUCUS stuff works great, and it not to expencive and should help.

44

Here's my suggestion: jack it up and grab the pinion flange, try to move it up/down. There should be ~zero~ movement. Even a tiny bit means you should look into pinion bearings! Don't confuse this with twisting movement, that will show you the R&P backlash but not the bearing condition. The backlash between the R&P is .003-.006 as measured at the ring gear, this equates to roughly 1/4" as measured at the outside of the pinion flange.

IMHO, if there is no up/down movement in the pinion, normal backlash as noted above and no metal particles in the lube, like 44 says change the gear dope and drive on.

HERE IS MY SUGGESTION:

Deliver it to Lansing Mi on Saturday June, 27 and I will give you free admission to the eVilGRM picnic!

+1 on rear diff bearings. The output shaft bearings seem to be a weakish spot on these diffs.

Jensenman wrote: Here's my suggestion: jack it up and grab the pinion flange, try to move it up/down. There should be ~zero~ movement.

Pretty much right behind where it attaches to the driveshaft, right? Easy enough to do, then if that's cool (I suspect it will be), everything will be in position to change the diff fluid and see if that fixes it.

You guys recommend Lucas over Redline? I imagine either one will work fine.

Foxtrapper, the noise only changes in frequency with speed. It's also a completely constant pitch at any given speed. Not rhythmic or rumbling at all. Just a constant: "wwwwwwwwwwwwwwwwwww".

Lucas for any that make noises and or street driven, high dollar red-line for perfect units.

Salanis wrote:

Jensenman wrote: Here's my suggestion: jack it up and grab the pinion flange, try to move it up/down. There should be ~zero~ movement.

Pretty much right behind where it attaches to the driveshaft, right? Easy enough to do, then if that's cool (I suspect it will be), everything will be in position to change the diff fluid and see if that fixes it. You guys recommend Lucas over Redline? I imagine either one will work fine. Foxtrapper, the noise only changes in frequency with speed. It's also a completely constant pitch at any given speed. Not rhythmic or rumbling at all. Just a constant: "wwwwwwwwwwwwwwwwwww".

Exactly, right where the driveshaft and differential flanges bolt together.

I have no experience wioth Lucas stuff, the Redline I use in the Abomination's RX7 diff is rated at 75w90 but seems a lot 'thinner' than conventional 75w90. I dunno if it whines, the racket from everything else sorta drowns that kind of thing out.

New theory on the car: wheel well liner.

Hung out with my dad, and he rode along in it for a while. He said, "That doesn't sound like a gear noise... that sounds more like something's rubbing."

And he said it sounded like it was most likely coming from the front wheel well.

When we stopped, he felt in the front wheel well, and there was a spot at the front of the wheel well liner that was worn through, right in front of the tire. His theory is that air pressure is pushing it back against the wheel at speed.

I'm going to tear out the liner and see if the problem goes away. I like cheap fixes of non-issues.

I like when things like that happen, hope that's your issue