We have a 7 seater Carens 2

We have a 7 seater carens 2.0 diesel automatic. We have it a year and a half and the brake pads have been changed twice in that time, 2 callipers have been changed, 1 unseized and the 4th is fine. About 3 months ago the 3rd calliper was unseized, pads changed and a full service done. Lately its been acting like its under pressure or losing power regardless of how many is in the car. The brakes or callipers hardly need to be done again? On the dash is an orange light in the shape of a tap with 'check' underneath it, we didnt get a manual with the car so have no idea what the light is. Also when you get up to 100kpm a rapping noise comes into the car and when you brake to slow down it sounds almost like a whirring sound and sometimes a light squealing comes in it when driving like as if a stone is caught in the brake pad but our mechanic has checked it over about 2 weeks ago and could find nothing wrong. Any ideas what is going on? Also we have never had an auto before so how much different are they to manuals on brakes, fuel, power etc?