whistling transmission

Here's a new one.

Got a detriot M60 with twin disk transmission in this boat.
When coming out of forward into neutral we are hearing a "beuuuuuuuu" sound. Like one of those yo yo whistles. Transmission oil levels are normal. All systems functioning normally and no error codes are being generated on the ECM.
Any thoughts anyone?

Is the transmission shifted with compressed air? Air throttles and shift cylinders will sometimes have solenoids that make noises when expelling air.

Just a wild guess/question.

No, it is just a standard cable shifter. And this is definitely a new noise that was not present previously. I had someone else suggest that it could be the turbo winding down, I'm going to see if I can pinpoint the location on a shakedown today.

Yes, I too thought of the turbo but you said transmission and I assumed you had already done some pinpoint listening.

Even so, sounds can "travel" and seem to come from places they don't originate.

If it's the turbo, it could simply be a loose clamp or it could be a defective waste gate.

Hopefully you can take someone with you that can drive the boat while you investigate.

It might help to take a long nozzle funnel with you to use as a "stethoscope". The kind of funnel used to add transmission fluid to a car works good and even better if you attach a piece of hose to the end.

They sell both at pretty much any auto parts store on the way to the marina.

Good luck with your test ride