i'm still convinced that it is the sound of there feet hitting the floor. everytime i hear the sounds it seems to match up perfectly with a foot hitting the floor. for example watch when there is around 3:46 left. here we see crocop kindof faking a punch he has some quick foot movement and we hear the sound a couple of times as his feet hit. i also watched from the 3:23 portion on until 3:14. all these sounds also seem to sychronize with crocops feet hitting the floor, the third one being him putting weight on his right foot to dodge sanchezs right hook.
I think they just got a new floor for the octogon that is rather noisy as you can hear this exact same noise in other fights as well(Rampage vs Eastman). If need be i will find the exact points this happens in that fight as well.
"When I lose, I get my butt kicked. When I win, I be doin' the butt kickin..." - Quinton Jackson