Phantom Brake Squeal?

[SonOfMaw]

After a week or so of faultless driving, my new M3 LR AWD suddenly started making horrible brake squealing noises from the passenger left rear wheel as I pulled away, in time with the wheel rotation. As the car warmed up it seemed to reduce, more so when I switched to reduced re-gen and used the brakes a bit. Happened every time I'd go a distance and then stop for 10-15 minutes. So I reluctantly went to the app and booked an appointment in the hope they'd be able to pinpoint it and do a fix - I'd read about broken brake pad clips being a possible source of the noise.

Lo and behold the next day it's all gone and no noise what-so-ever. I'm going to leave the appointment open for a few days in case it comes back, but I wonder if anyone has a clue as to what it could be? I'd have thought something like a broken brake clip wouldn't just "fix" itself?

 

[Dangerous Fish]

Probably just a stone or debris thrown up from the road stuck between the brake disc and back plate.
Nothing to worry about but by all means leave the booking open a couple more days.

 

[MrBadger]

A break squeal when reversing was quite a common problem when damp. I think its only gone away for us since using hold mode (for first few months, this was not an option) - we have a downward reverse off our drive so squeal was very offensive to our neighbours. They did find and fix a fault, requiring brakes to be rebuilt, but it was only temporary respite. Whilst diagnosing, it was suggested that I used lowest regen setting just to give the brakes something to do occasionally. That seemed to make a bit of a difference too. But I suspect, lack of brake use due to regen is going to lead to some issues being common, including debris build up.

 

[Dilly]

If it’s a small stone or debris, reversing and braking usually clears it

 

[Dangerous Fish]

A break squeal when reversing was quite a common problem when damp. I think its only gone away for us since using hold mode (for first few months, this was not an option) - we have a downward reverse off our drive so squeal was very offensive to our neighbours. They did find and fix a fault, requiring brakes to be rebuilt, but it was only temporary respite. Whilst diagnosing, it was suggested that I used lowest regen setting just to give the brakes something to do occasionally. That seemed to make a bit of a difference too. But I suspect, lack of brake use due to regen is going to lead to some issues being common, including debris build up.

Yes, plenty of owners on the FB groups with awful looking discs complaining about the state of them, but some of them have done 10,000 miles and never used the brakes properly. Understanding how a car works and what you need to do as preventative maintenance is a thing of the past now so expect to see a lot more of this type of complaint.

The reversing squeal happens particularly with the rear pads as they are are slightly offset in the caliper and wear unevenly, so brake dust builds up more on the trailing part of the pad and that can cause squeal. I have track pads in my P3D and on an ICE car they would be horrendously noisy at low speed, but I don't hear a peep out of them for three reasons:

1. I use hold mode all the time so don't use the brakes at low speed
2. They get a very good workout each time I drive on track and that keeps them healthy
3. I'm inspecting and cleaning the pads and discs much more regularly than most owners so I'm doing preventative maintenance each time

 

[Adopado]

If it’s a small stone or debris, reversing and braking usually clears it

Yes, I've had that several times over the years with a couple of different cars. The loudest and most appalling brake sounds can sometimes turn out to be the easiest to resolve! Broken stuff doesn't tend to spontaneously resolve so this would be top of my list too.

 

[SonOfMaw]

Thanks for the feedback, I'll keep my ears open, but hopefully it's a simple issue that's sorted itself. Otherwise the car's been faultless since I picked her up.