The "roar" is the fan clutch not disengaging. When you first start the engine cold, you might hear it for a couple of seconds, but then it should go away. There have been a lot of problems with aftermarket fan clutches, so genuine Nissan is the way to go. The squeak "may" be due to a bearing going bad in the fan pulley bracket, Nissan P/N: 21046-EA200. This is another part where there have been issues with aftermarket replacements, so it's best to stick with genuine Nissan if it is your problem.
http://www.nissanpartsdeal.com/parts-li ... ?PNC=21082
Nissan did have issues with belt squeak on these Pathfinders, as well, and released a TSB. The bulletin stated to check the P/S pump alignment and adjust as necessary to have the belt ride properly on the pulley. If that was okay, they stated to replace the serpentine belt tensioner and the drive belt, which was updated to a slightly shorter length (which causes increased tension on the belt). On the aftermarket, they usually refer to it as the "enhancement kit."