2016 MERCEDES-BENZ GLC300 Suspension Problems

Often after starting the car, inside the car there is a gas smell that we have to closed the vents as it becomes unhealthy until the smell goes away, it last up to 10 minutes. I have taking the car to my mechanic who specializes on Mercedes and could not find any leaks and/or anything wrong. My other issue is that during the raining season when I put my foot on the breaks it makes this loud sound like an airplane landing that I have to release and press and release and press so the car will slow down. My mechanic have done multiple inspections and finds nothing wrong. My third issue is the suspension, driving on freeways at speeds over 55 mph I feel a lot of shaking between front wheels and I can feel every single bump. Again, my mechanic has found nothing wrong that even checked for...