I've only broke in 30 or 40 engines but I've never experienced any high knocking vibration when breaking a new engine.
It is not hot glue!!! There are so many industrial adhesives available that are way superior to "hot glue" that no manufacturer would ever want to use it. Your engine shouldn't cause any more severe vibration the first tank than the 100th and if there were enough additional vibration to break the engine loose then the firewall would never have lasted in the first place.
basmntdweller