When accelerating you can hear a whistling sound similar to slightly open window on high speed, but if you remove your foot from gas immediately sound disappear, step again it comes back, so it's pretty much connected to stepping on gas pedal, sound go higher when speed reaches >38mph, but if you listen carefully sound is present even on lower speeds but not much noticeable, I am sure its not bearing or transmission since that doesn't make since when sound disappear if foot removed from gas pedal.
Whistling sound when accelerating on 2005 Honda Odyssey
by nawafpower in Louisville, KY on December 16, 2013
ANSWER by ziptie12 , December 16, 2013
Final drive gears in transmission worn. Could stay like that for a long time. Have checked for excessive play at inner axle joint on drivers side and if no leak from axle seal , then you should be okay for a long time. Not all that uncommon.