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Old 05-14-2010, 10:24 AM   #1  
VistaBlue
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Default Grinding Sound Coming From Rear End

When I'm driving, there is a horrible grinding, metallic sound coming from the rear end. It almost sounds like a spring compressing, but I've already confirmed it's not. At first, I thought it was the rear springs compressing when the rear end squats a bit on take-off. But with more testing, I have found the sound is present in these situation:

1st gear: 14-16 mph
2nd gear: 19-21 mph
3rd gear: 23-25 mph

Obviously these are rough estimates, but you get the idea. This is how I have confirmed it is not a spring, and why I am now more apt to believe it's within the gearing in the rear, as it happens at different speed, similar RPM, and in multiple gears. All tests done with little to no throttle applied, to make sure I wasn't causing the car to squat at all.

Anyone have any idea what I should do? All help appreciated.
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Old 05-14-2010, 10:57 AM   #2  
BruceH
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If you are still under warranty get it in to the dealer. Does it make the sound coasting with the clutch in or in neutral? If I was to guess right now I'd say you have a bearing going out. It could be something as simple as debris riding on your brake caliper too.
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Old 05-14-2010, 11:39 AM   #3  
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I made an appointment for service on Monday. The only reason I'm looking towards the gears is because it's happening at roughly the same RPM, and ONLY at that RPM. I haven't been able to test it out-of-gear yet, I'll attempt later today. Thanks for the reply.
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Old 05-14-2010, 12:21 PM   #4  
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Does it go away after the engine and exhaust warm up? There are a few rattles/grinding sounds that are related to engine RPM harmonics. Upon heat up, the harmonic response changes slightly and in most cases stops rattling. One that I had was resolved by torqueing the axleback clamps tighter. There are also heat shields that like to rattle plus a TSB on a seperator plate associated with the tranny that likes to rattle.
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Old 05-14-2010, 12:55 PM   #5  
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Doesn't change when it's cold / warmed up at all. I'm liking the idea of engine harmonics being associated with the rattle - that ties into my current theory involving the engine RPM. Down low, a little shake = rattle. Hoping it's something simple like the TSB.
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Old 05-14-2010, 03:15 PM   #6  
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Something very different just happened. REALLY hot out today (90+), last couple of days when it started were very cold (~40-50 degrees). Just started the car, sitting with it in neutral, clutch disengaged. Rattling like crazy just sitting out of gear!

It stopped as the engine went down to regular idle RPM. Just playing with the throttle, slowly building revs or quickly, dropping slowly or quickly, I couldn't reproduce the rattle.

I also got an exact RPM it occurs at because of this. Both at idle (when just started) and when in gear - it is exactly 1250 RPM.
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Old 05-17-2010, 09:29 AM   #7  
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Do you have an aftermarket axle back? After I installed my Macs I noticed a matallic noise coming from the rearend. It was nly under excelleration and ocational chatter over rough road or bumps. It would get slightly worse when the car was warmed up and really bad when it was hot out (when it was really hot 90+ it would do it just idling). After looking all over I noticed that the front hangers on the exhaust only had about 1/8 inch or so of clearance from the hanger brakets and the cars normal vibrations were enough to make the hanger and the bracket bang together.
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Old 05-19-2010, 05:42 PM   #8  
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I figured I might as well give this closure to my situation! Dropped the car off at Ford on Sunday night, got a call Monday morning with the tech asking me if I had tried to fix it myself. I just said, well, no of course not! He said, well, we found a wood chip wedged between the exhaust piping and the body, removed it, and the sound went away.

So yeah. With all the construction going on in my area, apparently a wood chip caused me to get so scared! Imagine that
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