Intermittent Grinding Noise

[IISPEEDYII]

Hey guys wondering if you can help me diagnose this. Lately when I am driving, but not all the time, while under moderate/heavy acceleration I hear a grinding noise coming from the passenger rear side possibly. The way I could best describe it is the sound of a chain saw chain clanking. I can't really pinpoint it exactly, but that is side of the car is where I am hearing it. The sound then goes away when just keeping the same speed, like once I stop climbing to the speed limit. Any ideas on whats causing it or what it is?

 

[USMC_TOP]

Have you looked under the truck yet? Look for something loose by grabbing and pulling on stuff. Lots of sway bar junk back there and the exhaust. Also check your lug nuts

 

[Bigunit]

...and passenger side motor mount and exhaust manifold (cracked or broken bolts).

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[USMC_TOP]

Good call BIG!

 

[Bigunit]

That's what mine turned out to be 2 weeks ago...same intermittent noise...broken passenger AND driver-side motor mounts and broken exhaust manifold bolts...all fixed now and ready for more wheeling.

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[IISPEEDYII]

That's what mine turned out to be 2 weeks ago...same intermittent noise...broken passenger AND driver-side motor mounts and broken exhaust manifold bolts...all fixed now and ready for more wheeling.

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Thanks for all the info guys! I'll get to looking at it tomorrow when its light out.

 

[alrock]

I think Big's on target. You may have something tied to the engine. When you're on the gas, the engine is being torqued and stuff is moving, hitting and making noise. When you're off the gas the engine rests and is no longer hitting anything.

 

[IISPEEDYII]

I think Big's on target. You may have something tied to the engine. When you're on the gas, the engine is being torqued and stuff is moving, hitting and making noise. When you're off the gas the engine rests and is no longer hitting anything.

Yeah but when Im maintaing rpms theres no noise, or is that what you're trying to say and I'm just mistaking it for something else.

 

[alrock]

At a steady throttle the engine probably rests a bit and lowers into position, or at least away from what's causing the noise. Acceleration really works the motor mounts and if they are shot then they can move around a bit.

What I'm saying is Bigunit's diagnosis may be right on target and I'm just adding a bit of color to his play by play call.

Here's a bad but not totally failed motor mount. The tear in the rubber goes from about 8:00 to 1:00. Once it made it to the 2:00 position it would be really bad. But you can see with the open space how the motor is allowed to move somewhat inside the mount. Once that tear is complete it can move a lot more.

 

[IISPEEDYII]

Alright thats what I'll look for, and the manifold too, but its sounding like its going to be the mounts then.

 

[alrock]

Manifold bolts could have broken too with the engine rocking. I think my previously failed mounts (like 4 failed ones on the passenger side) contributed to the cracking in my exhaust manifold. Keep in mind the noise could be elsewhere too. Less likely, but worth a look, is to check the propshafts and make sure the u-joints and CV joint aren't failing. I'd make sure the exhaust hangars are intact and the exhaust is not hitting the frame.

 

[SuperBuickGuy]

I just repaired every heat shield on my H3, those makes a rattle and/or a clunk sound. I repaired all of the exhaust manifold bolts (exhaust leak sound). But most recently it was the front differential. It started as a howl, but then a light knocking sound at 1400-1600 rpm. I figure by the time I'm said and done; I'll have the ultimate how-to book just by printing everything I'd detailed in my SAR H3 build thread. Granted, I use mine pretty hard and it has a lot of miles; but still, I think I've had about every major failure there is.