+1 on Art's comment. NH sickle bar bines have adjustable guards and one or more are too tight. One reason I prefer the SCH design. The guards are rigid. Adjustment is self compensating.
You might also have a problem with the back ledger. If it was worn, the 'crash' could have pushed the backside of the cutter sections up on top of the ledger. That binds the sickle, creates heat and causes the bar to squeak.