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Help! I’m hearing a horrible sound

I’m hearing a horrible sound when I drive my 2002 Trailblazer. It has 250,000 miles and we have babied it since the first day we bought it. I’m hoping it will last another year. The sound I’m hearing happens intermittently. I took it by a mechanic, and of course it didn’t make the sound. It sounds like you are driving over rumple strips found on the shoulder of expressways. I then feel a “drag” and it goes away. Any clue on what’s going on?
thank SO much!!!

Given the miles on the truck, I’m guessing some kind of joint in the drive train. There are U-joints on the drive shaft (to the back wheels) and CV joints on the front axles. When the joint “vibrates” you get the noise. It vibrates intermittently based on harmonics, and movement of the axles so sometimes you hear it and other times you don’t. A garage should inspect these joints with the car up on a lift. The loose joint should be easy to find. I’d take are real good look at those u-joints on the front to rear drive shaft.

Whatever joint it is, it isn’t going to last long like this so it should be found and repaired real soon.

Uncle Turbo’s theory has merit, but I want to offer a possible alternate diagnosis.

When you reach a steady cruising speed, your torque converter should go into “lock-up” in order to eliminate the slippage that normally takes place at lower speeds. This lock-up is so that you get a slight boost in your gas mileage.

However, when the solenoid, clutch (and possibly some other parts) that control torque converter lock-up are not functioning properly, you will get a “rumble strip” feeling when you hit the speed at which lock-up should be taking place.

You have not told us whether this vehicle has an automatic trans or not, but if it does, the problem could simply be a need to replace the Torque Converter Clutch Solenoid (TCC) , which is connected to the transmission case. Have your mechanic check out this possibility, or–better yet–go to an independent transmission shop.

Do not go to AAMCO, Lee Myles, Cottman, Mr. Transmission, or any other chain operation unless you want to be told that you need to overhaul the entire transmission.

Thank you so much for advice Uncle Turbo and VDCdriver!! I will have my mechanic look at your suggestions. Have a great day

Perhaps you could tell us something about the conditions under which this occurs. We can - maybe - guess that its only while the vehicle is in motion as you mention drag. But is that so? Is this only when the car is moving? At about what speeds? While accelerating only? Decelerating only? Maintaining speed? Can you make it happen? If so, how?

Do you have a check engine light on?

The rumble noise usually happens at lower speeds around 25-45 mph. I have never heard it on the expressway. The slight “drag” happens right before the rumble stops and a bit afterwards. When it happens you can hear it when I take my foot off the acceletator and when I maintain speed. It usually lasts about 5-10 seconds. I can’t make it happen.
thanks

I’m right there with VDCdriver then in terms of a TCC lock up problem. Brace yourself for expensive. However, you can hope for something simpler such as a drive shaft issue as UncleTurbo mentioned. Either way a good, local transmission shop is the kind of place to be.

Shoot if that’s what’s wrong with it how much do you think it would cost?

and could I live with it for awhile?
thanks :slight_smile:

First you would want to make sure that’s it. Do you have something like an “O/D Off” button? It might be associated with something you’d use if you were going to tow with it. Turning that off often disables the TCC lockup. If it does you could leave it off for normal, everyday driving, though you’d want to turn it on for any long-ish highway trips. If you don’t have an O/D Off of some sort, if you were to tap the brake when it does this it should stop it & that would be a good indication.

IMO, its worth it to pay a good, local trans shop an hour labor to look at it.

Thank you!!!

Yeah I think I’m with the torque converter lock up theory. It is attempting to lock up and when it does, it will “drag” because there is no more slippage between the engine and the transmission. If it is the torque converter going south, you would want to have that fixed. If it blows apart, it will send the debris through the transmission which will require a trans overhaul. For just the converter I think you’re in the $3-500 range. For an overhaul you’re in the $2000 plus range.

You can confirm the converter at least by slipping it into neutral when it starts to rumble. If it quits, its a good chance that’s it.

Can you feel any vibration in the steering wheel? Does it seem to be coming from the front or the rear? One side or another? Is the car 4wd, and if so what setting is the selector on?

Vehicle is 4-Wheel drive capable. However, control unit is faulty and was deactivated in January 2006.
There is a noticeable vibration, visual and feel, in the steering wheel.
Vibration seems oriented more from front of vehicle vs. rear. Can not determine if it is coming from one side or the other. We took it on a two hour trip over the weekend and problems were VERY apparent when we came off the hwy. Most of the weekend we experienced the same problems. We have an appointment Thursday. I just want them to check things out becasue last time I took it he didn’t hear anything. (of course it was acting fine) So should I have them check the U Joints, Torque Converter and CV Joints?
thank you

BTW After the weekend trip it’s been fine.