need a log of precisely that happening while recording the log to say something
also 91 oct ca nt be good enough for the stock tune and advance multiplier should drop accordigly
Also if you take a look at knock correction table of stock tune you see the "worst" knocking area for Subaru is right at low rpm high load so when you jump on throttle suddenly on low rpm
I d bet you have one of the first revision of the 2013-2014 tunes, which don t have a timing revisions from Subaru during fast transients/blips so timings can get too high and cause pre ignition and the most common failure caused by this is the oring in the DI injectors that disintegrates
i don nt think one is able to hear the proper engine "knock" sound just by blipping the acceleator, but you can clearly hear if the oring popped, by a loud popping dry sound when you quickly blip the throttle
Without a video of the sound and a log anyway is difficult to guess
EDIT: oh well the OP is providing while i was writing this, so i ll wait for the logs