I'm guessing it's a vaguely-recent game thing where vehicle engines "stop" when not moving (unless it's some mod I have installed)? It's annoying to hear the helicopter engine stop/start a lot while hovering.

Is this a known issue? If not I'll check my mods.

Not necessarily a known issue although it sounds like the kind of thing I wouldn't have noticed. I will check it out. I have another bug I need to check out with this mod, too. I work in devops so work has been super crazy with all the remote work going on. Will check it out when I can.

I am not able to recreate this issue. Is it still happening?

Yes, last I tried (probably at least a month ago). It seems that after opening the map, doing something, then closing the map, there's a chance one hears the vehicle-start sound again.

BTW why is the fuel usage so much greater while accelerating than while hovering? With real helicopters there's not so much difference (maybe a factor 2 with a REALLY powerful helicopter; with most I imagine there's barely any difference, then again this one can accelerate pretty quickly).

Yeah, I should probably change that. For the most part I left the original fuel mechanics from Kumpu's mod, but you raise an excellent point; I will probably change it. I don't know that much about the fuel usage of helicopters, other than that I looked up the typical fuel use over time of an apache and applied it, I think, to the accelerating usage. So unfortunately your request probably puts me in the position of making it use MORE fuel when hovering. :) But I like being honest to physics.

Regarding the start-stop sound I'll try opening and closing the map to see if I can recreate it.

Try as I might I just can't seem to recreate this problem. The map properly "muffles" the sound for me, whether I'm taking off, landed, flying, whatever. Is there anything else you can tell me about the situation in which this happens?