volume down pushing more sound

Hi guys!!

on my mpc 500 I've notice this bug or whatever, when I play more than pad it seems the global volume goes down. If I continue playing for example the snare when I stop to hit the kick the volume become harder and harder

did somebody know something about it???

thankssss

no compression at all

master comp OFF

even other pad/tracks dont have comp on it

with master volume at 0db and the volume know totlly up it keep stay under -6db on the input mmixer