Knightmare.com

Been rewatching knightmare recently and noticed that there appears to be an odd twanging sound that doesnt seem to correlate with on screen events.
Its hardly noticable but when i use headphones its quite obvious when you spot it.
Does anyone know what this could be?
Its driving me nuts >:D I retty much signed up here in a desperate search for answers.
Thanks in advance for any help

Difficult to comment without being able to hear the sound. Are you sure that it isn't a problem with the recording?

Cool username by the way! Hope you'll stick around and join in the forums.