I recall that when starting these RB211s, if you don't get that resonating sound, as you occasionally didn't, the engine would always go on to suffer from a stagnated start with rising EGT.
I always listened specifically for that sound, and if I didn't get it when I needed to, I closed the start lever, allowed it to run back down on the starter, then when stabilized, re-introduce the fuel/ignition, worked every time.
If I allowed it to continue to the stagnated indication, the resulting EGT would be much higher and would therefore take much longer to cool back prior to restart.
Did that for years in Air Pacific in those very nice (leased QF) 747-200s they used to run.
EW73