What is this loop? Tomorrow Never Knows Take 1 sped up. Let's solve the mystery!

What is this mysterious loop originally from?
Is this the correct original speed?
What instruments are we hearing?
So many questions!
Please leave your theories and guesses in the comments.
"Tomorrow Never Knows" take 1 from The Beatles Anthology 2
This is what the loop they used sounds like sped up.

[@LearnToForget]

Te high-pitched sound is a Guitar and the loudest sound is a mellotron ,an organ ,and a piano playing the C chord at the same time

[@paunchstevenson]

The problem is the high pitched notes don't sound like a guitar and nothing here sounds like a piano. I also hear what sounds like a timpani keeping a beat. This is so bizarre and puzzling.

[@LearnToForget]

@@paunchstevenson I tweeted Giles Martín the son of the Beatles producer George Martín, I'm up to date seeing if he responds

[@paunchstevenson]

Thanks, I'm interested in his explanation.