If the sound object does not meet the length requirements (too long / too short), what suggestions do you have? Are sources given attribution?

Yes, the object does meet the length requrement. Attributions need to be given.

Is sound the primary means of signification? If not, how might this be improved?

Yes, the sound is the sole means of signification.

Does the sound object convey the same meaning or message as the text / image objects? If not, what suggestions do you have? Are there any seemingly unintentional variations in aesthetics?

Yes, it does convey the same meaning as the text object. From the sounds, it is easy to tell that there are cops involved in an operation, you can hear the police radios in progress. 

Does it sound good? (transitions in remix / appropriated material? sound clean? minimal noise / static (unless purposefully meaningful)? sounds work well together? appropriate levels?

The quality of the sound is good and it all works well together. The levels were a little high for me but a listener can easily remedy that by turning down their volume.

What does the sound object convey when listened to on its own?

The sound object conveys the feeling of a clandestine operation in progress, especially the background music.

What suggestions do you have? Both about this object as a solo piece, and in the context of the portfolio?

There is a place in the score, in the beginning, after the first song, the music ends kind of suddenly. Blending or fading the music out might be helpful. In the context of the portfolio, you seem to have already made the changes to the text object and now the two pieces work better together.