Blower is so loud it is easily heard above the engine! So we never run it.
We had the same problem when I installed our new blower system. We couldn't stand it on the first cruise as it was much louder than the engine. I pulled the wires from it after the first half hour.
The intended purpose was to remove heat for the alternator cooling and to also remove heat while the engine cooled down after running on a scorchingly hot afternoon when we were preparing for a night at anchor.
My two design errors were:
1. I used a Shurflow Yellowtail 3" blower. Screams like a banshee from the get go. I saw mention here that a forgotten production boat was using Detmar blowers. Tried the two of them side by side and the Detmar was quieter.
2. In the original design, I also used an aluminum drier vent which conducted the sound beautifully. Drove anyone near the boat nuts.
I substituted a rubberized fabric hose from Defender.
The fan exhaust .....................
..................... is now quieter than the engine.
Check your assembly and if it uses either of these items, you may be able to reduce the noise.