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Old 06-27-2012, 11:36 AM   #600
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What I Drive: 2012 blue focus SE

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Yeah! where's my paycheck?!
I've been trying to figure this one out for a while now, and to take a bit of heat off the techs, it's more complicated than we think. First of all, it's sounds suspension related, so they check all the suspension parts.... No problem found. If you look around under there, all is tight as can be. So I think the suspension is a dead end, and here is why based on these clues:

1) the sound is a rattle, or sometimes when it's a clunk, it's really just the first part of a rattle or a very very short rattle. That means that two things are touching each other that should NOT be touching. Not something that needs to be tightened.

2) when it's colder, it's more likely to actually sound like a rattle, and when it does there are about 4 cycles to rattle, and they are at a frequency of about 8 cycles per second. That means that the pieces are moving pretty far, like a couple millimeters or more. Anything with any tightness at all will never move that far.

3) when it warms up, my sound all but goes away, a least it is much less obvious. When you first get in after it's been sitting for a couple hours, it's pretty bad. The weird thing is that when it gets warmed up, that process takes about 15 minutes or more. So it's not water temperature, and it's probably not exhaust temperature (although it could be! I'm not sure how long it takes for exhaust pipes to come up to temperature but I suspect it's not more a a couple minutes..right?), but it seems like its related to the general temperature under the hood. So some parts are maybe tightening or more likely actually moving apart as they get warm. That's not suspension.

4) it's not the calipers either, although that is the most obvious thing that gets hot, and gets tighter when it gets hot. It does it while braking as easily as when coasting.

5) I have a manual trans, and I can make the sound happen by lugging the engine by starting in 2nd or third gear! It's the EXACT same sound as when going over small bumps at slow speed. By the way, the bumps most likely to trigger the sound are NOT bumps, but places in the pavement that suddenly drop DOWN, kind of the opposite of a bump. Since I can make the sound by lugging the engine (when it lugs, it moves around in the engine compartment more) it means that something is touching the engine, or the trans, or the exhaust system, and it either should not be touching, or is not tight enough. As I said above I would say its more likely that the pieces should not be touching.

6) here is big clue..... Nobody can find it by looking under there! That means that either everyone is totally incompetent, dumb, or uninterested.....EVERYBODY? That seems unlikely.....or it means that everyone is looking in the wrong places, and that seems plausible to me......or it means we all have a different sound which is also possible.....or it means.....

7) the sound itself is the sound of metal touching plastic. If its metal moving against plastic, it's probably the exhaust moving. If its plastic moving against metal, it's probably some line like a brake line or fuel line or bundled wire that is moving. There are a LOT of suspended wires hat are meticulously insulated and suspended so they don't rattle. I have insulated a LOT of those things and never found the one that is the culprit. Probably one that's not too visible.

8) things that make the same sound under the hood include:

the hood prop rod. Flick it with your finger and it makes the same sound. That's not it though!

The battery cover....also not it
The washer bottle....wrong
The under lining of the wheel wells and the plastic under the engine compartment.....wrong too, I insulated all this stuff

The actual hood, which I spent a LOT of time insulating. It rattles with the same sound but it's not the issue either

On the manual, the actual shifter is right on top of the trans and easy to see and touch, you can wiggle it up and down on it makes the EXACT same sound. I can't figure out a way to insulate it and still let it move freely. That could EASILY be it, but I don't know if the DCT has a similar kind of shifter. It's a weighted thing that swings side to side to select the gears in the trans. It looks like a fancy golf putter. You can move it with your hand, and it's pretty loose and has a lot of play......Hmmmmmm. If you start out in first gear and then accel hard but push the clutch in when you are still accelerating you can make it make the sound when the trans goes from stressed to not stressed quickly.....Hmmmmmm

All kinds of wiring and other random stuff hat I insulated to no avail

9) it's nothing that shows or is visible. You can't see the top of the strut towers without removing some plastic...could be there. Can not really see the exhaust very well either. Could be there......

10) the engine mounts have been mentioned, and that seems plausible given the fact that you can reproduce the sound by lugging the engine, but when the engine is stressed it seems to work great. If it were the mounts wouldnt it get worse as the engine is pushed harder?

The dealers and techs and engineers don't have the advantage of being obsessed with this minor rattle (it is annoying but honestly, it's pretty minor) like some of are:)
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