Possible transaxle noise

Hello
2004 Prius, 140k miles (owned since 50k). All maintenance done on regular basis.
Transmission fluid changed last spring at 120k with Toyota WS, also checked last weekend and its level with fill plug and clean.
Both left and right half-shafts replaced under warranty around 40k+ due to clicking... so they have 100k on them.

On a suggestion, I had the tires rotated (front to back).. no change.

Hopefully I did this right... link to audio file I created.
Coasting from 60mph to 45mph in neutral on smooth off-ramp, applying brake a little near end.
At the 3-4second mark the noise really comes in,

I stopped by a local mechanic, he took it for a quick drive around block, but didn't hear noise. (I told him it's heard when on smooth pavement at above 50mph).
He put it up on lift, verified the wheel bearings are fine. Said he hears a noise coming from where the left half-shaft goes into the transaxle(?). Said not worth fixing... just drive it until it gets bad.

Car is due to change oil, so this weekend I'm doing that and will drain the transmission fluid into clean container. If there's metal shavings/chunks on drainplug I know its done for and will just put the fluid back and get rid of the blue baby. I don't expect this, but who knows.....
While I have the car up on jacks, I'm gonna get in closer with a car-stethoscope and try to isolate source.

Thoughts? Things I should do?

I'll update & answer questions if you have any.

 

Did that to make a clearer audio recording

 

it's really annoying whine/growl... kinda like driving on a road with groves in line with vehicle direction.

 

Yeah, I see a lot of used trans out there for $300-600... but not an easy swap for an old DIYer.