I'm with @crip659, @UnhandledExcepSean, and @Ecnerwal.
The sound is your metal roof. You say the sound is random, but I'd wager that if you kept a "strange roof noise diary" and then cross referenced the sounds with outside temperature and solar exposure of your roof (sunshine + shade), you'd find a pattern so obvious it would bite you.
The most likely explanation is that steel (the most common metal used in standing seam roofs) expands and contracts at the rate of .08" / 10' / 100°F. If your roof has a 20' span, on a hot day your metal roof can easily heat up to 100° above ambient and drop as low as ~20-30°F cooler than ambient. As the temperature of the metal heats and cools during this diurnal cycle, a 20' run of metal can expand and contract by 3/8".
There is probably a spot on your roof that isn't completely free to expand and contract as the roof temperature changes. That restricted section builds up tension in the metal until the tension overcomes whatever is impeding expansion and then it breaks free, making fun noises.