Well sometimes numbers overlay on screen and cause you to see a number that you actually do not do. My invoker does around 6000-7000 damage per x, but sometimes show a number like 76,540 damage. And even with 600% cd it shouldn't hit that high. Other players have experienced this particular scenario I have mentioned.
However, I'm no help for the amount of hits/and sound that is replicated as I've told you before. I can hit faster than you, but never recalled unnatural sounds of hitting twice yet only hitting once. 1 thin g I can mention is if you are performing an unorthodox combo that even I rarely use, the hits do not hit albeit being right on top of the person. This affects very high attack speed users and sometimes cripple since you attack so fast they are midair/flinch/knockback that it misses them. If it isn't this then, I'm no help for this thing.