95 legacy stock 190K miles

I get that characteristic faint rattle sound of knock, pre-ignition, gas ping, whatever you want to call it at around 2250-2500 rpm under mild partial throttle conditions only, such as slowly accelerating or going up a hill.  Most pronounced using 87 octane and gets about 50% better with 93 octane. its still winter grade gas here but this has been going on no matter what the season.  Could this be a bad knock sensor - I know they can go bad and not throw a code. thx for any tips.

could also be carbon buildup in the cylinders.

 

Perhaps a SeaFoam treatment and knock sensor investigation to start?