Swift D, Premature Disc damage and Turbo Whistle

Hi guys, need some input on this ! Off late I'm facing a couple of issues with my Swift D(2008,Ldi). 1st issue Braking at high speeds(read 110 and above) on highways results in minor pulsation felt through the brake and slight cabin vibration too. This has increased a bit, and the presence is now felt at 90 or 100 KMPH braking. Everything is fine below 90 KMPH braking, what I mean ,is that if Im doing 60 and then brake , I dont feel anything. But at 90 and upwards , I do. Now the SA has diagnosed this issue as a imperfection in the disc after a test drive he took and he has advised replacement of disc along with brake pads for a cool 5k!!! :Shockked: I'm a little skeptical, as disc AFAIK last longer than the 30 K Kms I have used them for and the reason he has given me is that the car has gone through a bump. PS Im not facing any lack of braking power nor any alignment, balancing issue. I can easily take the car upto 140 smoothly , the issue starts when I brake. PS2 I have been advised to get the disc's " lathe'd/turned " but someone else told me not get them done as the brake will feel "spongy" after getting it done. Pretty Confused. Whom to listen to. Any pointers? 2nd Issue There is a whistling sound( louder than the usual turbo whine we encounter when the turbo does its job) During the speed band of 80-100. Here is the weird bit:- 1.After 100 the whistle goes and it only starts at 80. 2.Only happens when I approach 80 and go up with 5th gear engaged, and does not happen when I tried it with the 4th gear and approached 80 and went onto 100 although it is not recommended to be in that gear(4th) at those speeds. BUT the sound disappears with the 4th! 3.There is no whistling whatsoever in an other speed band except 80-100 EXACTLY! I tried maxing out all gears. 4.The whistle is high pitched like a jet taking off , its pretty darn irritating sometimes! 5.I have not got any turbo/intercooler cleaning done at the moment/in the past as the surge after 2k RPM is OK! 6.What I dont understand is , if there is any issue with the turbo then its should make such a noise at all ranges and not in a particular band. YELP!!!! ANYTHING would be helpful. GT500

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