Howling from drive

I have a 1989 5.7 Cobra engine and drive in my 1990 Donzi GT250.
I just had the u joints replaced as they where getting rough (vibration) when turning and trimming the drive.
Now after the u joint replacement I am getting a howling noise from the drive when it is in gear at between 850 to 1100 rpms.
The noise starts abruptly at 850 rpm and seems to fade out a around 1100 rpm.
When the mechanic replaced the u joints he said the gimbal bearing looked good and had plenty of grease and the inside of the bellows was dry.
This noise is only when in gear and at 850 to 1100 rpm's and is fairly loud and other than this the boat runs strong and smooth.
And like I said started immediately after the u joints where replaced.
Any ideas
Thanks

Did he align the drive to the coupler ?

He said the alignment looked good.

i would have to hear it. All outdrives make a whirling noise . You have enough fluid in the drive ?

Yes gear lube level is good and gear lube is clean.