I'm sitting on the ramp in Haley, ID (sp?) in a DA-20 with the wife of a Fortune 150 firm at the time, it's 95F outside and she asked me if I could "turn it down?". I asked her what she meant and she said " the noise, it's bothering my dog's" (a big old stupid poodle) "ears".
I then told her that the APU was keeping it cool inside the jet, to which she responded, " you're only the co-pilot, what do you know?". I told her she was correct, so I shut down the APU, walked back into the FBO and gave my resignation to the Captain.
I hope they got home.
fbh