a quiet, variable noise sounding like a whirling electric motor or mixer or pump occurs occasionally when driving. Its intermittent and not related to acceleration, stopping, or speed.
Could be a number of things. Air condtioners cut in and out. When you let the car run and stand beside it you can clearly hear that.
The cooling fans are thermostatically controlled and they also cut in and out.
A good A/C shop can quickly tell you if it is the A/C or radiator cooing system. It’s hard for us here to speculate exactly what it is.
If your Odyssey has automatic climate control it could be the cause of the noise. The doors in the HVAC system move now and then to regulate temperature and airflow direction depending on the system settings.
You didn’t tell us where the noise is coming from. Is it from under the hood? Under the dashboard? Under the car? Front, rear, left, right?