Your testing seems to confirm my experience......Spark doesn't make much noise. It is easily lost in the background noise, particularly at a little bit of distance.
Spark's small size and low level of noise makes it a good stealth quad. With my P2 and P3, i always had people walk up to me while I was flying to ask about the quad. The only time I've attracted attention with Spark was when I was practicing Gesture Mode. A guy came up and asked if I was praying to something when I had my arms in the air trying to Beckon Spark back! Spoiler alert.....I had to wait for the battery to die and Spark to land.
