2016 peterbilt 587 Engine break issue

I'm in the process of purchasing a peterbilt 587 with a cummins engine and when I was doing a test drive the engine break sounded really weird. It was like ttttttttttttt like metal being hit really fast and kind of loud it sounded unmuffled or something, even the salesman said that sounded weird. I drive a 2016 579 now for the company I work for it has the same engine and it doesnt sound like that at all. Does anyone know if that could be a big problem or an easy fix?

 

They havent shown me any records yet. I test drove the truck and afterwards they took it to the shop to get that fixed, so when I go back there on wed I will ask for it, if they dont want to give me ill go to the dealer and see if they can print me one also will pay for one online.
Its 2016 petevilt 587 it has 556k miles on it, it looks really good it drives good from what i can tell except for this engine break issue. Im getting it from arrow truck sales with a platnum 400,000 mile warranty through ntp.
How would I check the clearance do i have to take it to the dealer?

 

I will definitely read everything before signing anything, thank you.
Is there anything I need to check for once they get the truck back to make sure they did it right?

 

Yeah, true, I'll go see what else they have. If they dont have anything else in my price range ill take it for an inspection maybe get a dyno also before buying it.
Thank you.