550 S4 noisy drive train

I just purchased a 2012 550 S4 from the original owner. The machine only has 113 hours. I don't seem to have the shifting problems yet, although there must have been some modifications made as it will start in gear. That is not a problem for me and I have an old 4X2 with 1,000 hours on it and it always has grinned a little when putting in gear. so I'm thinking of making the modification so it will start in gear. My problem with the S4 is that the drive train has a very loud whining noise as it revs. The original owner told me it was always like that. Are these 550 S4's all like that? or do I have a problem?
Any info will be appreciated Thanks Larry