The problem was a small change contractors had made in the way the steel plate was attached. Phil Fish explains, instead of steel pins, which stay in place because they fit precisely, the contractors decided to use bolts that are simpler and much cheaper. Those bolts started shifting around, creating the popping and banging noise. With time, they could have broken. Yeah, it was a cost-cutting maneuver and maybe it's working, maybe it's not working.
Fish seems inclined to consider it all an honest mistake.
But Dan Hogan, one of Prine's colleagues from Northwestern, isn't so charitable. Again, a minuscule cost when you have a multi-million dollar structure. Oh, at least. It carries the eastbound lanes of Interstate 94 across the St. Croix River. Last year, Fish was shocked to discover hundreds of cracks in its steel trusses.