"2 - The knocking noise are the brake pads - they move freely within the caliper, but they've stressed that this is nothing to worry about. To me, it doesn't seem like it's a brake pad problem as the noise gets louder when I go over speed bumps, but who am I to question the mechanics with their infinite wisdom(!) Granted, it potentially could be nothing to worry about, but having paid a lot of money for the car and raising this issue with Lexus on several occasions, they've failed to address the problem - something I'm not happy about as they sold the car to me in this state."
Similar happened to me. Had the 'rusty' brake 'clips' replaced and the brake pads skimmed to make them flat and even again, and the problem was fixed.
No.3 - Loose wire?
No.4 - I assume under warranty.