Ok, 1500 miles on the Falkens, they drive straight and track nice.
But, starting at ~ 45 MPH I get a "thrum" with a 1 1/2 second period. What I mean is it goes "thrum...thrum...thrum...".

And it is felt more than heard.

It can be seen in the rear view mirrors.


It DOES NOT change with speed.
It DOES NOT do it on all road surfaces.
It DOES NOT shake the steering wheel.
IT DOES NOT seem to be tire hum.
It feels like it might be coming from the rear.
I have had all 4 re-balanced. No change.

I will (finally) install the stabilizer in the morning to see if there is any change.

And I'll slip it into Neutral at 70 to see if there is any change too.

It's the strangest thing...

I respectfully wait for any help?

 

I had a similar problem with a volvo sedan years ago. Turned out it was sympathetic vibration. In this case it was a loose mount on the exhaust pipe. It would only do it on smooth surfaces and between 50 and 70 mph. Probably not much help there but it's all I've got. You've made me curious though. If you think about it when you find the problem drop me a PM? Good luck!

 

I'll try to remember to PM you.

Any help is appreciated.

I don't think there is enough mess in the exhaust to make this pronounced a vibration. It can be seen in the rear view mirrors.
And it is felt more than heard.

 

It was not the dampener.

It is less noticable with a full tank of gas.

Any takers?

Guessers?

 

Well lets see a full tank reduces the thrump..
I'd have to bet with the added weight the car is sitting a tad lower. The shock is now traveling on a different area of the cylinder? My first guess would have been a tire issue but then you said it didn't change with speed. I'm still guessing its a tire issue?
Bill,

 

Thanks, Bill. That is my first choice, but it is exactly the same at 45 MPH as at 80 MPH.

Tread squirm? I remember that from the early days of radial tires. But now???

 

You probably already know this. Checking for out of round or any flat spots. Jack her up just off the ground , put in gear then take a piece of chalk and ever so slightly work it across the tire while spinning.

When applying the brakes does it get worse? Maybe rotor or brake pad issue?
Had a similar problem with my Jeep but it was more of a "Growl" thought it was a tire issue but turned out to be a bad wheel bearing.

 

Next thing. I've got a buddy at a quick lube place that'll give me 20 minutes on a lift for free.

 

Max, I've got the same problem at around 70. I've got after market wheels and 295 30 19s on the rear. This did not occur with the old setup. The strange thing is that it is not constant, but has that "thrum, thrum, thrum" thing going on which tells me it is not a wheel balance issue. I'm about ready to get new rear tires. We'll see if that will solve the problem.

 

Hi Max
I did have a tire now & then in my past yrs. that were defective within the belts. Best way to rule this out is:

a. Block the front & rear of one tire to prevent any unexpected roll away of your car.
b. If it's one of the rear wheels your checking, put trans. in neutral & keep the hand brake OFF. Obviously a level surface is req. for this type of check.
c. Jack each wheel up one at a time just to point where you can turn it freely by hand, but no further.
d. Take any very squared off block of wood (2 x 2 of 4 x 4 etc) with a length that runs at least across the entire tread or more & keep firmly placed on the floor just about 1/8 inch in front of the tire. SLOWLY turn the wheel by hand & see if it the 1/8 inch equal distance around the entire tread holds.

Since you mentioned you can feel it rather than hear it, this will rule out a defective tire. I had my tires react this way when I would rotate them. Some belts didn't like to reverse direction, but I know your case doesn't involve having rotated your tires.
Hope this helps.

 

Oooohhhhh.... you are a good man! Let me know as soon as you know!

 

I'm a bit of a machinist, so when i've got this on a lift, my practiced eye will be able to see <.010". And across the tread too. I'll especially keep an eye on the rims. since they are aftermarket too.

Thanks though!

As an afterthought, since these are one-direction tires, I might just mount them up "backwards" and take it for a spin. Might be interesting?

 

Doesnt change with the speed

Must not be a tire shape / runout issue. It sounds like a resonance that has changed amplitude with increased mass - gas.

It has a period of several seconds but the same noise, sounds to me like a resonance with the exhaust sustem and the tire vibration. You have not reported the coasting in neutral change or lack there of. I suspect that you will see coasting makes it very much lighter in sound.

Try this, please go down the road and change the gear ratio, like go into 4th and maybe 3rd to see the effect of moving the engine speed away from the tire speed. Should make the thrumm go faster or quicker in period.'


Makes me think of Don Knotts and the Thrumm that the fish made to disable the submarines and torpedos. Mr Blimpit or something - your old youll remember.

Enjoy, woody

 

Max, you say it does not happen on all road surfaces. Do you notice a difference between driving on asphalt and concrete? What type surfaces does it occur on?

 

Here you go

http://www.youtube.com/watch?v=xdK3z3Uqiws

Woody

 

I remember seeing that movie when I was short! Thanks!

 

Ok, I tried coasting on the way back from the tank fill up. At that time it decided to be quiet. I just finished a 6 hour marathon wash/clay/polish/wax and will wait a couple of days for clear weather to try it again. I'll try neutral/coast and downshifting when I have a nice thrum going. Thanks, bud!

 

It happens on both asphalt and concrete. But in Alabama any given road can change ages twice in 2 miles. Makes deciding this problem pretty difficult!

Thanks!

 

Are you ruling out its any type of vibration noise? A "thrum" to me would sound like a vibration.

 

It's definitely a vibration. It is felt much more than heard. It doesn't shake the steering wheel, doesn't change from straight to curves and doesn't change with speed changes.

Weird. Any thoughts?