I'm taking part in an experiment in Electronic Voice Phenomena. No voices so far however, last night I recorded a two minute segment which included two 'knocks'. Before anyone asks, I was sitting quite still and did not hear them until I listened to the playback.

I've uploaded the section with the knocks on below. You will hear me say "Hello...is anyone there?" (Yeah, original I know!). A few seconds later you can hear two knocks. Spooky eh?