So I’ve noticed that while backing up and tapping on the brake pedal I hear a knock on the firewall right before the pedal makes pressure. Mostly hear it when stopped. Is that a significant sign of booster failure?
it happens only when backing up?
No pretty much all the time.
hmmmm… before calling the brake booster the issue, try looking around to see if maybe something is loose or something like that. see if you can pinpoint the sound.