Audio Meters' Inconsistency

Hi,

I have a shot where someone walks away from the camera. I added a footsteps sound effect, which I wanted to  become quieter as the person walks away. However, the footsteps in the effect I downloaded are very random, going from loud to quiet to loud again etc.

I want to ENSURE that each footstep is quieter than the last. I assumed that Premier Pro's audio meters would be the perfect guide, showing me the exact volume of each individual footstep. However, I have found that if I play back a given footstep more than once the meters often show different dB values each time. I am very confused by that.

I am aware that the bar represents average volume and the yellow line represents peak volume but that doesn't really explain why the value shown by the meter changes from one playback to the next. 

Any help would be appreciated,

Thank you.