Haha, I noticed this when listening to this through headphones at 4AM once...but bad recording?! Out. It's one of their best tracks from the period!
All I could possibly say in any sort of 'defence' is it's a B-side isn't it? And it's not ALL through the track. Were it going to be put on the actual 'Unforgettable Fire' LP I'm sure they would have cleaned it up.