[X1_230d_First]

Hello Everyone, this is sort of my first-post. I have 2010 BMW X1 with X-Drive (auto transmission).

I see an issue in my car wherein it gives a jerk at lower gears (I can feel the jerk specifically when the gear changes -- like a small thud).

A little history on car:-
-- The front 2 tyres & rear tyres are not of same brand
-- I recently changed the brake pads (both rear & front)
-- the car has about 55,000 miles on it
-- I went to local BMW dealer, & they said that the front drum and disc are going out of sync which could cause the issue, I don't agree with them because the time when I see this issue, there is no brake applied.
-- I called the place from where I changed the brake pads - as per him, it could be an issue with brake calipers which have lost calibration, hence, the brakes are not getting apart properly and causing jerk - again, not sure why the issue occurs at lower gears?? - I don't agree.

I'm totally newbie to cars - I have read few forums which point out to issue with engine firing, valves going bad, steering issue?

I'm lost & already spent quite a bit of money (showing at 2 places) to understand the issue. Can anyone help me?