I did this test a few days ago with a free-floating UA (meaning 100% health forever). I turned everything off except sensors and life support in a DBE, went into silent running and spent around what seemed like 10 minutes before my heat approached 100%. I was at 500m from the UA. Nothing appeared or happened, unfortunately.
You didn't record the sound (or does anyone have very long recording of the sounds)?
Longest I've got is io one.