The Stovebolt Site Forums The Shop Area Engine Shop Clunking sound from down under

Well, I've tried to ignore this sound but it's starting to really bug the U-NO-WHAT out of me. When the truck is cold this noise sounds like something is loose as if my horn was barely hanging onto the firewall or the oilbath cleaner is flopping around. This noise only appears when the truck is in motion, so if I'm at a stand still and rev up my engine when it's still somewhat cold, the sound does not appear. Most importantly the noise disappears after about 5 minutes of vehicle movement.....

So it seems like something else such as the clutch, tranny, or what else gets warmed up and the sound goes away. As a passenger, my son says it seems to be coming from (he points to his toes) that area ? Minutes later during driving, it goes away.

I've looked underneath to see if anything was obvious but no luck, especially since the sound goes away after warming up. So it must be internally ? But where ?

Again, I don't think it's the engine since I cannot hear the sound when reving it. Only during movement.

How the heck do I trouble shoot this ????

Exhaust manifold bolts, manifold to downpipe flange bolts, or baffle in muffler?

When the connection heats up it expands and stops rattling.

Never mind, just read your post again. Not sure.

I don't think its either of those Tony for you cannot hear the sound if you're at still and rev the engine which the 3 ideas you suggest are defineately engine related which I think one would be able to hear while revving. The sound only appears if the truck is moving and the sound is not what I call a constant sound. It's sporadic.

Each time I hear it, it seems to be coming from the back of the engine, that's why I keep looking towards the clutch or maybe tranny ?

Argh :confused:

If it is only making the noise when you are moving could you jack up the rear wheels, put some jack stands under the axle, put it in gear and listen for the noise using a 3 or 4 ft. piece of garden hose. If there isn't any noise doing this then jack up each wheel, spin it and listen for the noise.

What does it do when you depress the clutch while moving when the truck's cold? Accelerate or back off? Apply the brakes? Lots of things to try. Does it make the noise in reverse? Does it change when you shift? Or is it directly speed related? What about when you turn the wheels? Or apply the brakes without backing off the throttle?

Could it be tires? Don't know what you have, bias ply will take a set when sitting then thump until they warm up. I'm throwing a lot of questions out because there are so many possibilities to eliminate.

Fred T,
You came up with lots of good questions, which I'm going to start answering tomorrow morning after a chillin nite. Don't think it's the tires because it's not a consistant wheel revolution sound. It's a lot more metally and very sporadically. Not consistant with the RPM's of anything running such as flywheel, tranny, etc. If I had to invision something after having a couple glasses of wine, the sound seems to be coming from the foot starter rod supporting bolts or something in the starter. What I am really saying is that it "sounds" like it's coming from that area. Maybe my imagination is going a little too far.

I also like racecarldad's idea which if nothing else works, I'll do this weekend.

Fred T,
Thinking more about this...I heard the sound when in reverse while it was cold. So no I don't think it's speed related. All you other questions will be answered tomorrow.

You know, can it be my front right wheel bearing going kaput ?

Do you hear it only in reverse?

I've had some pretty clunky U-joints in the past, but that doesn't sound quite like what you're describing....

No, I hear it when driving foward also, like driving 3-4 block. Then it disappears. U-Joints ? Hmmmmm!

I had a similar prob w/ my 235. I took the engine out before I found out the cause. My hunch (after I removed the engine) was the heat riser in the manifold. My noise sounded like something (bolt or other metallic object) rattling, like something was loose. Never did find it though. Clamp a pair of vise grips on the heat riser rod and see if the sound changes or goes away. Mine drove me nuts too :mad:

I've had a lot of cars where the countershaft in the tranny does exactly this complaint. Kind of a rattling, random trashy noise. Check the trans fluid level and go from there!

Best of luck!

Probably not. U-joints usually just give you one big clunk. From my experience....

You're getting some good things to check though.

Guy here at work just had a noisy u-joint in his burb. Drove him crazy and couldn't find it until he pulled the driveshaft and took all the load off the joints. Had on roller set on one joint that hadn't been getting grease in it. The other 3 rollers on that joint were still good.

I had a right front wheel bearing that was bad and the sound really wasn't all that speed related. One of the balls had shattered and it made a rubba rubba sound while moving but once you hit 25 it didn't seem to get any higher or louder.