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My 2016 3 GX has developed a loud rattling/knocking sound on cold startup. This lasts only for 20-30 seconds on acceleration. It appears to be coming from under the body, not the hood. Anyone else experience this, or idea what is causing it?
 

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I get a little of that with my 2017, pretty sure it is normal for a straight 4 to do that, they are inherently unbalanced so there is a lot of shake when they are cold. I would bet yours is just shaking the catalytic converter or the heat shield.
 

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I get a little of that with my 2017, pretty sure it is normal for a straight 4 to do that, they are inherently unbalanced so there is a lot of shake when they are cold. I would bet yours is just shaking the catalytic converter or the heat shield.
Thanks for that! I didn't think it was likely serious, but as I have only 1 month left on the dealer warranty I thought I should check here
 

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Heat shield rattle was so bad on the Subarus I owned I had my friend use his torch and we tore them off.
 

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This could be normal as until the blue temp light turns off and the idle lowers the lifters do make a bit of a louder ticking noise than when the vehicle is warmed up. Also, there are these really dumb little like heat blanket patches riveted to the manifold covers and the rivets are known to rot out, could be one of those little blankets, I’ve pulled plenty out of the bottom of the early 3rd gen 3’a While doin oil changes. I would also check the muffler to midpipe flange as those donut gaskets do tend to lose some material.
 

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This could be normal as until the blue temp light turns off and the idle lowers the lifters do make a bit of a louder ticking noise than when the vehicle is warmed up. Also, there are these really dumb little like heat blanket patches riveted to the manifold covers and the rivets are known to rot out, could be one of those little blankets, I’ve pulled plenty out of the bottom of the early 3rd gen 3’a While doin oil changes. I would also check the muffler to midpipe flange as those donut gaskets do tend to lose some material.
Thanks for this. My next cold startup I will wait until the blue light goes off before any acceleration to check for your suggestions. The mid pipe flanges may be the culprit, as the sound does seem to come from under body somewhere. Thanks again.
 
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