Quote:
Originally Posted by humblebrz
Background info on car: 2014 Brz 6MT. Stock with no aftermarket modifications. 20,000kms. Subaru oil changes and maintenance. After sitting in the cold Below 0 celsius for approx 4+ hours the start up results with what is heard in the video. The knocking noise sounds like it is coming from the passenger side.(this is where the video is taken) additionally the knocking isn't present until after the car is idling for 5+ minutes with the heat on, rear window defroster and heated seats turned on. If those accessories are turned off, no knocking noise is heard. The knocking noise is not present when the vehicle is stationary reved at any RPM or if it at normal operating temperature. I have tried to diagnose this without success. My local dealer just replaced the cooling fans because they said one was warped and hitting the shroud... needless to say the noise is still there.
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I'm 90% sure this is belt "slap". My current 06 impreza does this and my previous '12 legacy did this on cold starts. Hard to tell through cell phone speakers but here is another good comparison video
Its just caused by your belt being stiff and the timing belt tensioner fluid being too viscous from the cold. If it goes away when it warms up, dont worry about it. If it gets louder or worse look into having your tensioner replaced