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oscillating hum or 'whaaa' sound

7K views 36 replies 15 participants last post by  briandors 
#1 ·
Hey all.

Just picked up a new GTO Saturday. 2006 M6 SRM with 18000 in Chicago area.

So the first thing I noticed on the test drive was that from 30 to 45mph there is a slow cyclical or oscillating hum, sort of a resonance, it sounds like whaa whaa whaa whaa and the cycles are perhaps every 1-2 seconds. Its not an even pitched hum or whine, like when my first GTO went through two differentials.

At the price I negotiated, I couldn't pass it up, it was well cared for overall. So I drove it home to Cleveland.

I'm thinking of crawling under it tonight and checking the tires and perhaps driveshaft?? Other ideas? It still has the original 18" Bridgestones on it (unless the owner was very aggressive and this is the second set). But I had it up to 100mph on the way home, there is no vibration at any speed, if it was the tires I'd be surprised to only get noise with no shake.

I'm confident its not the brakes.

Maybe there's poly bushings in the drivetrain causing the resonance?

If I can't determine anything it will probably go to Backstreet Performance in Medina.

Thanks for any ideas.

Brian
 
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#4 ·
I've got a bit of that pulsing noise also in my new-to-me '06. Some tires are noisier than others and some cars are also, I guess. My car came with Goodyear Eagle F1 All Season and I have no idea if they might be part of the problem. (I don't know why the last owner went with A/S. This is Texas. We only have one season.) Seems like the sound comes slightly more from the rear.

I do know that my Grand Cherokee is light years more quiet than the GTO w/stock exhaust. Does anyone suspect wheel bearings or maybe noticed things quieting down after new bearings? I might try a few strips of Dynamat around the inside wheel wells and trunk area. When it comes to new tire time, I'm definitely going to shop the noise factor for replacement tires.
 
#6 ·
Seems to be all stock underneath. Do the stock driveshafts say "MZ" on them?

The tires were around 31psi, I brought them to 35psi and didn't note any change.

I hear a little bit of differential whine -- my ears are well tuned to that sound from experience with the previous GTO. But it's a constant whine not an oscillating sound.

I can only imagine that a slowly oscillating noise means there are TWO noises clashing together, question is, which two. Maybe I'll rotate the tires tonight, the rears are notably more worn than the fronts.
 
#7 ·
For what its worth, I've had that noise ever since I bought mine at 85xxx miles. I now have 125xxx miles and its still there but never caused me any problems. I've just accepted it. If it ever gets on my nerves I just jam the gas pedal to the floor and let the exhaust note cancel it out.
 
#8 · (Edited)
Do you have contact with the original owner or previous owner? If you do... would get all the information about modifications to the car from them.

Stock drive shaft should be a two piece black... with rubber donuts on both ends and a carrier bearing in the middle. It does have a white tag on it labeled MZ. Like the one in the picture below I provided out of a for sale thread here.



Its worth checking to make sure your carrier bearing bolts are tight and all the driveshaft bolts/nuts are tight as well. It very well could be tire noise, I know when tires get to the end of their life they normally get louder.
 
#9 ·
Yup, that's my driveshaft there. Same color, two piece, donut, etc. I also see the same "MZ" sticker.

It doesn't SEEM like tires, but when two sounds combine and kind of reverberate against each other, it's hard to tell.

I'll check the bolts around the driveshaft.

I bought it from a Ford dealer, but they handed me the title and it shows the previous owner's name and address, so I may tactfully try to make contact with him.

Thanks.
Brian
 
#11 ·
Not to beat a dead horse, but I wanted to make sure I was clear on the noise I am hearing. It's NOT like a 4x4 pickup that is raised and running on huge mudding tires. Although that's an oscillating wawawawawa kind of sound, it oscillates fast and in direct proportion to the speed of rotation of the tire.

My sound is a much slower cycle, perhaps one "waa" per second at 35mph, and it is not consistent in volume, one "waa" could be loud and then the next softer and then back to loud... or you might get two loud ones and then one soft... it's slightly irregular both in its tempo and its volume. Hence my feeling that I have two sound waves clashing.

I'll rotate the tires and check the driveshaft bolts tonight.

Thanks for everyone's help!!
Brian
 
#12 ·
Mine does it, too. It's not really a vibration, just a wha-wha-wha-wha-wha hum. Aroudn the same speeds too, when the exhaust isn't very loud, and neither is the wind or road noise. To me, it sounds like my right rear tire. I'm riding on not-so-sticky Cooper Zeon rubber, and I'm pretty sure those are bottom-of-the-barrel noisy tires.
 
#13 ·
Aftermarket exhaust? Could possibly be exhaust drone.
 
#16 · (Edited)
Hmm. Wheel hub maybe? Try going about the speed when it starts, and then aggressively going left and right. See if it gets quieter going one way, and louder the other as you load and offload weight from turning. Best to try in an empty parking lot :)

May also need to get the drive shaft rebalanced. I'd doubt that though.
 
#17 ·
The only non stock part I have found on the car is a K&N Filtercharger airbox, which I'll be posting up for sale soon as I don't like hearing the throttle body whistle and fortunately the previous owner put the stock box in the trunk.

I have tried the left-right-left-right and don't hear any change, so I don't think its a wheel bearing.
 
#18 ·
Might be the tires then. See if there are any local GTOs that are willing to swap with you for 5 minutes so you can find out.
 
#19 ·
I picked up a subtle harmonic hum like you're describing back when I put my Pedders bushings in @ 8k miles, though mine only does it at 75-80mph. I never found the cause & it's not really very noticeable, so I figure it's an inherent NVH thing that the stiffer bushings allow through.

Probably not much help for your situation.
 
#21 ·
Ima drank a barr an gunnit! Ay boy, watchdis! Put yerr head up unna thar and see ifya harr uneethang.
 
#22 ·
^ :lol:

Yeah tracking down odd sounds can be tricky to say the least. There is a huge section devoted to diagnosing Noises/Sounds in the official Helms repair manuals for the GTOs. Its thick too... but it can be very useful if you happen to have a set of them.

If you do not have a set of them... I would highly recommend any owner that works on their car regularly should purchase a set. You wont have to or always need to use them, but they are very nice to have for when you do need them. The forum is great... combined with the helms manuals, even better.
 
#26 ·
Any update on this or are you still waiting?
 
#27 ·
They called a couple days after I dropped it off to say they had narrowed it to the differential. Probably some bearings inside it.

They pulled the diff and sent it to a local rebuilder along with a "rebuild kit".

Either while they still had it apart, or maybe after they put it back in, they still heard the noise and have decided it's the needle bearings. They've called Pedders and GeForce and apparently nobody has a set of needle bearings in stock in the USA. So now we're waiting on a boat that is supposed to arrive about a week from now. At this point hopefully I have the car back and fixed in two weeks.

Not sure how much needle bearings cost, I assume BSP didn't order them right off the bat because they were trying to save me some money.

Rich has been very nice to deal with.
 
#29 ·
Call Andy @ CSP to see if he has any
 
#30 ·
Brian, Andrew forwarded me your email.

I responded to check w/ Gforce LOL

I am also out of new INA needle bearings...but I have several sets of good used ones I could ship to Backstreet if you're in a bind.
I will mention it's highly unusual for these to go bad and make any noise. Hopefully whatever 'rebuilder' they used actually put all new bearings in there, and all races. Not just the cones that are in the rebuild kit (I'd guess about 90% of the 'rebuilt' or gear install diffs i have seen the races were not changed out).
 
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