Take a look at the size of the engine and the huge bypass fan. It will by size alone subject to more noise than smaller engines. The procedure used on the B-777 engine start that adds to the noise perception is that we start them both simultaneously. The APU is strong enough to easily make the dual start.

The Boeing 777, particularly the 777-300ER, is known for its distinctive and powerful sound primarily due to its GE90 engines, which are some of the largest and most powerful jet engines ever built. The noise often described as a "sawing" or "buzz" sound occurs during takeoff when the tips of the massive 128-inch fan blades exceed the speed of sound (Mach 1), creating tiny sonic booms. Additionally, the 777 is an older design compared to the 787 Dreamliner; while the 787 uses "chevrons" on the engine casing to mix air and reduce noise, the 777 relies on high-bypass technology that prioritizes massive thrust over modern noise-dampening aesthetics. In 2026, the newer 777X is entering service with the GE9X engine, which is significantly quieter than its predecessor while maintaining the "power" that aviation enthusiasts have come to associate with the 777 family.