HT & DRUK
Jet Jockey
I'm pretty sure they would have heard it, felt it because of yaw changes or certainly seen it on the engines gauges.
Just a FWIW I certainly know of one case where 3 "pop" surges on take-off (actually during the rotate) produced
no visible effect on the "gauges" (EICAS). However the Flightcrew sure as heck felt and heard the "pops" and since it was night
they were rapidly made aware by some others on the aircraft and also on the ground that "something" had happened...
It was full power takeoff, hot and high airport, and with a significant cross wind.
AFAIK the whole event lasted < 2 seconds, ops were subsequently confirmed as normal by both Flight Deck indications and satcom with the datalink equipped engineers at "Mission Control". I guess despite that some here would suggest that the crew should have thrown the aircraft back on the ground "just in case".
Oh, and it was on a 4 holer - I am not going to get a debate about whether the aircraft continued to destination or not and whether if they continued the rights or wrongs of crossing the Atlantic, if that was involved.........