Here's a possible explanation for those film rips.

From "The Sounds of Star Wars" book:

PG.53

008 Hatch Sizzle and Explosion

Quote: "At one point while Burtt was working in the basement of Park Way, he was handed the color work print. At that time, Lucasfilm had only one work print of Star Wars, so the utmost care was used when handling it. "I thought, 'This is really valuable; my future's at stake here," says Burtt. "So I threaded the work print up on my Movieola very carefully. I checked all the rollers and sprockets to make sure it was okay. Then I pressed Go - and ripped the films to shreads! Oh, boy. So I spliced it back together and tried to pretend it didn't happen. But all the screenings from then on always had this jumpy spot right when the stormtroopers come bursting through the door of the Blockade Runner."

http://www.chroniclebooks.com/soundsofstarwars/

http://www.amazon.com/Sounds-Star-Wars-Jonathan-Rinzler/dp/0811875466