A new amateur video of the WTC 2 just came out of the woodworks seven years after 9/11 that even though the view of where the "Flight 175" should be seen is obscured, no sounds of an approaching plane can be heard before you see the explosion coming out of the back side of the South Tower. However, airplane sounds are heard at the very end of the video:
The beginning of the video shows a middle-aged male "hippie," who claims to be an architect, reassuring a female bystander that the plane crash they claim to have witnessed would not be enough to knock over the tower.
The video seems to edit twice to different scenes even though there seems to be a continuous audio feed through out the entire video.
The hippie then is heard saying that he witnessed the 1st WTC crash and says it was a "medium-sized passenger airliner." A bystander then interjects that the plane the hippie guy saw was a Boeing 737. The hippie then says he couldn't identify the markings of the plane when asked by another bystander.
Interestingly, the source youtube account was just set up for this one video.