Hard to describe sound

[Onexl85]

After I get on plane, and start to lower the rpms .......there is a hard to describe sound coming from the drive it seems. Almost like a blower whistle. My mechanic said its the exhaust. Does that sound possible?
Rebuilt merc 5.7 tboltv. Alpha 1 gen 2

Btw u joints are new as well as the gimbal

 

[Scott Danforth]

If you back off the throttle to about half does it change the whistle immediately? On my boat, you can hear the secondary throttle opening as the intake starts to whistle.

If it's your exhaust, you could have dropped a flapper and that is causing the whistle.

 

[alldodge]

Can you record and post on utube?

 

[Onexl85]

I think I may have dropped a flapper......just had the marina replace them while everything was apart. One was rotted and the other wasn't there. Do I have to remove the drive and get it out of there? Or can it wait