I have a MY 2013 V6TDI.
Within the first year of ownership I noticed the seat was constantly moving. I am 108Kg, and figured it was just me...or as some wag has suggested my big fat BTM was the cause. However, into the second, i would find the seat flat out in the morning after garaging it for the night. I thought that strange and reviewed the switching...took to the dealer...they found nothing...ok, what's the issue? Back to the BTM thing???
However, on a longer trip (300K) I was constantly having to readjust the seat back. Took back to the dealer (v3) and they thought it would be good to leave with them overnight. I did. They would review the mechanisms...hallelujah a warranty claim. The entire seat back was replaced.
Now into year 6 and the same clicking sound is coming from the back of the seat on long trips. Sounds very like a mechanism is failing or stressed. May be time for an upgrade...the newer V8 would be good...a dream.
I am not the only Touareg driver in Canberra with the issue. A Service "adviser" told me that it was likely because of the cold weather snaps in Canberra - oh really - this i a GERMAN vehicle where it snows much more than here

. Needless to say that was not impressive. Still the vehicle is one of the best things I have had for years...have had Triumph, BMW, Statesman and more, but this gives me everything I would want (except 300KW of course) and more...and my wife can even drive it (and she's < 5' and 55 Kg wringing wet).
So, I suggest taking back to the dealer and getting the seat back mechanisms resolved. Good luck.