It is a type of immediate correction pulled from the Subaru ECU. A common misconception is that Feedback knock is always detonation or the car running in a dangerous condition. Many things can cause Feedback Knock. The most common that we see is a loose heat shields and intercooler brackets. Since the sensor is simply looking for a specific frequency, all you need is something at that range to trigger it.
You should be aware of feedback knock, and figure out when and where it’s happening. Often it’s a repeatable condition. If you have more questions please contact us. Logs are very beneficial for determining the validity of the knock.