1) Does the AM have a resonance, or excess gain at 20kHz? I tried a dozen indoor/outdoor settings, and there is always a band at 20kHz. The spectrum below is inside a quiet room. 2) In most of the indoor, quiet room, recordings, I see a rising thin line in the 30-50kHz range, see the above spectrum, the five panels cover about 20 minutes. Could this be a form of self-noise? 3) The clicking noise, I saw on other posts that this is SD card writing? I only see this occasionally. The image below was from inside a parked car at night - very quiet. Is the suggestion still to get the "Extreme" version of the SD card? Thanks - I love the unit. Keep up the good work - you are making a lot of research possible.