As the crooks are leaving with the trailer the guard at the gate says the left rear inside tire looks low on pressure. If a tire there was indeed low, there's no way to tell if it's the inside or outside tire. In fact, previous and subsequent shots showed the tires look normal.
After Mathews has been in the helicopter for a while he's holding the handheld microphone to his ear, presumably listening. The radios don't work that way.