Different brake calipers has different brake pads compatibility.

https://www.brembo.com/it/Varie/RACING%20PA...gue%20(012).pdf
https://www.brembo.com/en/Varie/Braking%20S...Performance.pdf

Keyword is to find the brake pads compatible to your brake caliper.. abit lari you'll pay the price hefty

I'm using brembo gt6 and gt4.. the brake pads hard to find

https://www.m3post.com/forums/showthread.php?t=1855569

Not sure to post here or fast&furious
I own a bmw 3 series G20, recently decided to change the front brake pads outside rather than the usual bmw SC
However since changing it, firstly there is brake squel usually after driving for few minutes . It squeal when you brake lightly , and also sometimes even without braking you get very light squel as if something just touching . For some reasons when you just started driving the car it doesn’t have this , only after probably at least 5 minutes of driving .

Secondly I get knocking noise when braking as well. When the car is parked and engine is on when you step the brakes all the way down you get a knock when you depress the brake fully .
Also another time is after driving a while you reverse and the first braking attempt when you reverse definitely a knock
But the knocking noise at parked when engine is on is not there when you off the engine.
The brake pads according to the workshop is original bmw .
But I realized the part number is different from the part number shown online when I check using VIN
I was given part number 34106860019
While online check using chasis shows 34116890553

Not sure if these 2 are the same , as a workshop said one could be old part number another is new

70k

Actually I asked to change to exact sc spec
Anyway if your theory is right by right skimming should help ?

If u dun racing here n there, nornal driving, the rotor can tahan 100k one before needing to change 1..

Before change dun have, after change only have ?

That mechanic is u first time visit? Got check review before?

Skimming just removes the outer layer of the rotor to remove rust etc.. imho it's just an interim issue.
I also drive a performance car.. but i also face similar issue.. i found out brake pads and brake caliper need to be compatible.. dont beat to cut the cost.
I also face when slow brake you can hear a screeching sound when your pads gripping the rotor.

That issue is between rotor, caliper and pads.
Don't look at the brake lines not related one

Checked review
By right bmw does 2 brake pads for every 1 rotor
Front first time changing pads can reuse still

Rear differnt story la coz every 15k will the pad will due

Installer forgot to apply brake grease behind the pads and piston callipers

I had the same problem before.

my mechanic adviced me, if you're changing brakes, make sure to change the "same pair" of pads and calipers and mount (forgot the name). it could very well be like what your mechanic said - old and new part no, but your other brake parts might not be fully compatible. blame bmw for this.

i learned the hard way - brake stopped working when you really need it to work. changed the whole thing and don't change mechanic shop.

Yea 2 and change 1 is correct..
So u 70k.. this is 2nd lo?

So what shall I do now

Cao k is ?
I wanted to give him he said no need he is very familiar
But browsing online I found this
https://www.loyalparts.com/shop/bmw-34-10-6...ake-pads-front/

Seems both part numbers are interchangeable ?

So what shall I do now

Buy g20 under warranty?
If yes then do all at SC
If can't afford then axia ftw