Finally, got it checked at Oberoi Fiat, Noida. The whistling sound from front brakes is almost gone. Brake pads were scrubbed with some material and some greasing done. That resolved the issue. During test drive, noise started coming from rear brakes now. It was very surprising as it was the heard for the first time and after rectification of front brakes. I don't know why it happened as the technician didn't do anything with the rear brakes as I was standing near the car for almost full duration. That was also resolved through same procedure. Explanation given was that rust was causing this, though I am not sure. Once the rear brake issues was resolved, I drove it for 20 odd Kms and no noise was observed except for a very faint noise[very very less intensity than earlier] from front brakes twice. Problem looks almost resolved to me more or less and will observe for few more days and decide next action. Overall, Oberoi Fiat was fine that they acknowledged the issue easily, looked into the issue without much botheration and were open to my test drive to check the issue. From technical perspective, I didn't find their technicians convincing enough. Experience with braking over the next few days would probably be the deciding factor to rate them. Their drivers  aren't good though. They slip the grip from clutch too often causing a lot of noise, too much of accelerator push and I had to ask them to take it easy. I felt very uneasy and decided to be with the car during every service from now. AND I met one of my colleagues at the workshop who helped me in deciding to go for a Fiat. He has got himself the 2014 Linea Multijet and had a niggle with the defogger which requires replacement of the rear windscreen. I dropped him home with him driving my Jet and he loved every aspect of it.