Marine Trader transmission noise

1988 MT 34 with SP135, bought it last year, ran it in the yard for about 10 hours between the fall and this spring. Launched and ran OK for about 5 hours. Two days ago when I started it up, noticed something like a raspy whine (similar to the annoying buzzer before oil pressure comes up) at idle and while warming up. Looked around, sounded like it was coming from the front of the trans. I increased the revs, and it went away. Cruised around for a couple of hours without any issue (yes, I checked all the fluids, and had replaced the trans fluid earlier this year).
Yesterday, same problem, but even louder - noise started about 1 minute after motor start. Seemed to be coming from the same place, and I could even hear it conducted to the shift lever if I put my ear on it. It was louder than the previous day, and after a couple minutes of looking and listening again, it went away when I increased revs, and never came back during a couple hour cruise.
Anyone had a similar problem?

I have the eggsact same noise coming from my ZF gear on my lobster boat. It only does it if its alittle low on fluid , and its louder if the gear is cold (winter months).

It's been making that noise at start for over ten years and always runs fine the rest of the day , so I dont worry about it.

... maybe make sure you have the correct dipstick ?

You said you changed the fluid earlier. Did you use a different oil/brand? Just a thought.

The only time I ever heard that sort of noise from my Paragon tranny was when I revved it with a lowish fluid level. Quickly and permanently fixed by topping up. I wonder if you are mistaken in your fluid levels...? Checking the dipstick is correct was a good suggestion.

Do not know if the situation is similar but with our Twin Disc you must check the fluid level with the engine running at idle. Oil is pumped out of the tranny into the oil cooler when the engine is at idle. Reading the level with the engine stopped gives a false (high) reading. Only problem is it is difficult to read the level with the engine running because of "splatter" on the dip stick.

The dip stick on many marine transmissions are calibrated to take into account drain back when stopped. Our Hurths are that way and the book says check when engine off.