Popping/crunching sound after coming to a stop

lowrydr310 · 05-08-2019, 01:56 PM

I've had this issue for a while but only notice it when it's quiet inside the cabin (windows up, HVAC fan off, radio off). After coming to a complete stop at a traffic light, after a few seconds I notice a distinct pop sound coming from the rear of my car. This is different than the driveline clunk that I have, which I isolated to the center of the driveshaft somewhere (CSB or u-joints, that's another repair I'm doign soon). I thought it was suspension related, but I removed both rear wheels and everything looks and feels solid. When driving I don't hear this sound at all, it's only a few seconds after I completely stop. I can do a quick stop at a stop sign and accelerate right away, and I don't hear it.

One thing I noticed is that that a few seconds after I stop, the engine idle speed drops a bit. It's immediately after the idle drops when I hear this pop sound. This got me thinking that the brake booster is run by a vacuum pump, which presumably would generate less vacuum when the idle drops. So is this a caliper issue? Or is the DSC module altering the pressure on my brakes after I'm stopped? Is there anything else I should be looking at? According to my iDrive Service Info, I have an estimated 10,000 miles before I need rear brakes so I wasn't planning on cleaning the rear calipers until then.

lowrydr310 · 05-08-2019, 07:45 PM

Disregard what I said. It is drivetrain related. If I put the car in neutral before stopping and leave it there I don't hear the sound.

I'm guessing it's when the RPMs drop the load on the driveling is reduced and causes the sound. So it may be related to the clunk.

05-08-2019, 01:56 PM	#1
lowrydr310 Robot 3186 Rep 3,029 Posts Drives: 2006 330i, 2007 E93 335i Join Date: Apr 2013 Location: Souhtrne Califniora iTrader: (1)	Popping/crunching sound after coming to a stop I've had this issue for a while but only notice it when it's quiet inside the cabin (windows up, HVAC fan off, radio off). After coming to a complete stop at a traffic light, after a few seconds I notice a distinct pop sound coming from the rear of my car. This is different than the driveline clunk that I have, which I isolated to the center of the driveshaft somewhere (CSB or u-joints, that's another repair I'm doign soon). I thought it was suspension related, but I removed both rear wheels and everything looks and feels solid. When driving I don't hear this sound at all, it's only a few seconds after I completely stop. I can do a quick stop at a stop sign and accelerate right away, and I don't hear it. One thing I noticed is that that a few seconds after I stop, the engine idle speed drops a bit. It's immediately after the idle drops when I hear this pop sound. This got me thinking that the brake booster is run by a vacuum pump, which presumably would generate less vacuum when the idle drops. So is this a caliper issue? Or is the DSC module altering the pressure on my brakes after I'm stopped? Is there anything else I should be looking at? According to my iDrive Service Info, I have an estimated 10,000 miles before I need rear brakes so I wasn't planning on cleaning the rear calipers until then.
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05-08-2019, 07:45 PM	#2
lowrydr310 Robot 3186 Rep 3,029 Posts Drives: 2006 330i, 2007 E93 335i Join Date: Apr 2013 Location: Souhtrne Califniora iTrader: (1)	Disregard what I said. It is drivetrain related. If I put the car in neutral before stopping and leave it there I don't hear the sound. I'm guessing it's when the RPMs drop the load on the driveling is reduced and causes the sound. So it may be related to the clunk.
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