SMatyac

Hello!
I just purchased a 2005 C55, and whenever I floor it, above 3k rpm it sounds kinda like tires are screeching, or maybe can be described as a whirring noise.
it has a muffler delete so could it be an exhaust leak causing a whistle? Or could it be a bad diff? I have never owned a Mercedes before this one so I am not well versed in their problems and what makes a certain sound.
I tried doing a search but couldn't find anything that was described as what I am hearing.
Below is a link to a video I took to show the noise.
Any help would be greatly appreciated!
Thanks!