Air1727 From United States of America, joined Aug 2003, 328 posts, RR: 9 Reply 3, posted (9 years 3 months 1 week 1 day 12 hours ago) and read 1192 times:
Pressure differential between the high pressure air surrounding the exhaust and the low pressure high speed air on exit. During high end thrust, the boundary disturbance becomes so high you hear anomolies like popping or snapping sometimes. With higher bypass powerplants, the bypass/exhaust air mixture is more pronounced causing less disturbance.
In the Alaska bush I'd rather have a two hour bladder and three hours of gas than vice versa.