Prior to the Hotel+ Update, the lights flickered before Ambush arrived, albeit a bit longer than the lights do for Rush. Currently, the lights no longer flicker before Ambush's arrival, and players can now only rely on the sounds to prepare for Ambush. There is also a chance that Ambush will appear from the next room instead from previous rooms.
Due to a recent update, Ambush will break the lights again when entering lit rooms similar to its behavior prior to the Hotel+ update.