Zep's Ramble On-Am I hearing this part right?

Ok, take a listen to the studio version off of Led Zeppelin II. That rhythmic tapping that accompanies the acoustic guitar during the verses...listen to it at the beginning with the balance hard left (left on my PC anyway) to minimize the guitar, and tell me, did they flip the tape as it was being recorded? Because the tapping sounds backwards to me, which I never noticed before.
Or is it just a flashback?
Or is it just a flashback?
