PF was a glider pilot... but it is not clear at what level. A French Brevet B used to require a flight making two turns before landing. A Brevet C required a longer flight with a gain of height for 5 minutes, both followed by a safe landing. PF already held a professional pilots licence, so these first two grades should be easy. He may have done more. I do not know. (It may be that a very, very high performance glider must have Mach limitations, too...)
PF was concerned apparently, about speed and "odd speed/ sounds" (my words) .
It was noted several months ago that the power was reduced from TOGA to 61% N1 for a couple of seconds and the NU decreased for this short time, IIRC.
Then power was restored to TOGA for the remainder of the flight. Were any comments made, by BEA on this or is it mentioned on the CVR ?