RAC6 and RAC7 means is it a confirmation of the ticket ? as I am travelling today night and still the pnr status is RAC6 and RAC7 .?

Just seems strange they would need three very longs trains for that. I could see if the trains were a bit shorter but they were all pretty long. It was very odd. I tried to get pictures with and without flash but they all came out horrible. I pulled this from a video ( which also came out horrible) but you can see how all the lights looked like windows and how close together they were .

In the most simplistic way; the train sound in this case, is just bursts of air on and off. If the wind is coming from the source towards you, it carries these bursts faster so they don't die out before reaching you.