Backfire on deceleration?

We had an International 2 ton truck used to post guard. We would load up and get driven to our 7-8 different guard posts and change guard and move on. At night, the duty driver would let off the gas and compression brake about 500m before the site and then blip the throttle and it would sound like an 81mm mortar going off. That would wake anyone up! Funny how that only happened at night? :p