Azhari... Congratulations to your kid brother on becoming a Benz owner for the first time! Welcome to the club! Just reading your comments about the rear humming sound every few seconds. If you look at my previous threads somewhere around and others, we have found this to be vacuum leaks in the car's vacuum circuit which cause the vacuum pump on the right wall near the fuel filler door to over-activate in order to keep up the correct vacuum levels. Every few seconds it humms or buzzes, this is the vacuum pump noise. Usually the pump is not at fault. Costs at least A$1200 to replace it when its actually the vacuum hoses or the vacuum open/close rubber diaphrams which have gone bad and these are cheaper to replace. A techie here was over enthusiastic in replacing the pump as well as doing a full A$1200 sunroof repair job when another more honest techie did a grease job for a couple of dollars and fixed the sunroof jamming!!!! It pays to look around. I think the fuel pump does not humm or buzz, it has a high frequency hiss instead.