humming noise at low power descent

[Timbo2015]

When descending ( I mainly have noticed this on approaches to land) if I set the power to a very low setting, nearly all the way down to reduce speed, a low volume, humming kind of monotone comes on.  It will go on and off as I decrease/increase power about a certain throttle setting.  I have noticed this on the Mooney, as well as the 747 and 777.  I think it only occurs at relatively low airspeed.  What is this supposed to represent?

[alrot]

same thing

[MadDriver]

Isn't that a gear warning sound?

[Wingo]

Definately sounds like a gear warning. Check to see if your gears are extended, you'll find they probably aren't. The same happens when you extend flaps past a certain setting

[Timbo2015]

I have no idea what the first reply means.  The noise comes out of the computer speakers, not the joystick.

Gear warning sounds like a logical answer.  Next time I get this, I will extend/retract gear and see if that turns it on and off.  Thanks for your replies.

[Timbo2015]

That was it.  No noise with gear down.  Noise with gear up.