Brake squeal seems to be a common issue on BMW’s in general... My 340 was actually worse than my E90 in this area, despite being ten years newer. (As in you’d think they’d have figured it out...)
It’s such a common problem that TSB’s have been issued (for many/all of their models, I’m sure) to help dealerships resolve complaints about this. The fixes they suggest are to apply anti-squeal paste to the backside of the brake pads, clean the brake pads and discs, and to “bed” the pads in. I’d probably start by using anti-squeal compound and see if that helps. I’m skeptical of bedding and cleaning the brakes; these seem to provide only temporary relief from the noise.
If the anti-squeal compound doesn’t help, your best bet would be to use a different pad next time you do your brakes. Perhaps there are other fixes out there, but I’ve just learned to live with the noise. Thankfully it’s only an issue for you in reverse
