[Bart_Man]

Hello everyone,

I've owned my 428xi Gran Coupé since February of 2016 and I've noticed something that happens consistently when driving in the rain on the highway, and that's a dripping sound coming from the back of the car. It's a strange thing, it really is a trickling-water sound, it only happens when driving in the rain or when driving on a wet road surface behind another car or truck that is causing spray onto my car. Now, I'm sure this is just some aerodynamic effect that happens when driving in water, but I was wondering if anyone else has noticed this?

Thanks,
BartMan

[jeffc83]

Haven't noticed this myself at all but I have to imagine you are in the right track with that sound.

[Bart_Man]

Thanks for the reply. Yeah, mind you the 4 series Gran Coupé is a hatchback where the entire trunk lid plus also the rear window lifts up, rather than just the trunk lid of your 3 series. I wonder if it's just the water running down the channels besides the rear window, but it really does make a very distinct dripping/trickling sound. Also, in order to get a dripping sound, water droplets need to fall in empty space for at least a few centimeters into a pool of other water, and I don't see where water could have the space to do that in the back of my car. It's a mystery.

[jeffc83]

Originally Posted by Bart_Man

Thanks for the reply. Yeah, mind you the 4 series Gran Coupé is a hatchback where the entire trunk lid plus also the rear window lifts up, rather than just the trunk lid of your 3 series. I wonder if it's just the water running down the channels besides the rear window, but it really does make a very distinct dripping/trickling sound. Also, in order to get a dripping sound, water droplets need to fall in empty space for at least a few centimeters into a pool of other water, and I don't see where water could have the space to do that in the back of my car. It's a mystery.

Do you have a sunroof? Could possibly be the drain tubes.

Ah, yes, the hatchback will have different "crevices" if you will so beyond that, I'm out of ideas unless BMW installs a mini-bucket back there for the 4 series

[Bart_Man]

Haha, a mini bucket!

I do have a sunroof, yes. That's a good point, I suppose it could be that too, although it sounds like it's coming from the back of the car more so than from above my head. Then again, the sunroof drain tubes may go to the back, maybe?

[jeffc83]

Originally Posted by Bart_Man

Haha, a mini bucket!

I do have a sunroof, yes. That's a good point, I suppose it could be that too, although it sounds like it's coming from the back of the car more so than from above my head. Then again, the sunroof drain tubes may go to the back, maybe?

Yezzir! I understand all cars are different but I've owned at least 4 that have had drain tubes run through the roof to the back of the car under the rear wheel wells. These things can get clogged (especially if you park under trees) so I clean them annually to avoid potential flooding issues.

[Adamr916]

I know on my 3, I can hear the water running down the rain channel, but I never have had any get inside the car.

[Bart_Man]

Originally Posted by Adamr916

I know on my 3, I can hear the water running down the rain channel, but I never have had any get inside the car.

Yeah it's just a dripping sound but no water is getting into the car or the trunk.