I have a 2015 389 Fitzgerald glider. I noticed tonight that when I released the tractor brakes I could hear air continuing to flow somewhere. It is coming out of the exhaust port on the firewall. This truck has always had a delay between pushing in the knob and the brakes actually releasing, but now the air won't stop blowing out of the exhaust. The truck will hold 120 psi at an idle even with the air coming out of the exhaust, but I can't figure out why it is doing this now and I don't want something to happen while my driver is on the road. Thoughts?