[@King Tai]
twas the goal muh ha ha
basically since he heals rapidly what is being heard is the healing process going so fast you can hear it
and it sounds like running spiders XD

only exception is when he's stabbed by his weakness...that makes him sizzle and slowly the process down by a lot. So if he was stabbed through the chest the stabber gets the lovely view of the process in a slower motion. 

....its gross and i love describing it because the imagery is just fantastic XD