Surges on RB211s are not uncommon, particularly those with Trent cores due to the problem known as 'bird lipping'. It's a known issue, it happens, you conduct the necessary inspections mandated by Rolls Royce and if it passes then away you go. I'd be more concerned about a tyre burst than an engine surge. I've had one. My mate has had one. You say "Oooh, what was that bang? I think we had an engine surge. Stop." Like I said, no biggie.