>>12334058>>12334065The honk is not absolutely an indication of something having gone wrong, but it's not a good noise to hear from a rocket engine, it means there's a slight level of combustion instability inside the lip of the expander bell which is causing the bell itself to vibrate.
This is not a healthy thing for a rocket engine and it can damage the engine post-shutdown or cause it to explode post-startup as was the case with the early F-1's.
There are a couple ways it can be addressed though, you can slightly reduce the length of the bell to reduce flow separation, include baffles on the powerhead, or create a slight inward turning lip at the edge of the expansion bell to keep the exhaust flush with the wall.
If Raptors are having combustion instability issues, it's not even remotely an insurmountable or dealbreaking problem, worst case scenario they'd have to sacrifice 1-2% maximum efficiency in exchange for 100% reliability, not a bad trade.
