ive run in to some sound issues with my xp3's maybe they are what your hearing.
1 i have sometimes had air in the filter after cleaning them.
solution.. added water to force air out
2 spray bar whistle
solution drill out holes a little bigger
3 super loud hum from undertank
soultion ( i had a hollow space in the tank stand floor that acted like a drum) i filled it with 2x4 to reduce the airspace no more hum)
4 louder hum when doors were open
solution open spaces in the back of my tank stand aswell as open doors let aot of sound out, when i inclosed the filter under then tank here was less noise
5 ive noticed that things the touch the filter vibrate so if there hollow they conduct the sounds
solution place the filter on rubber or do not allow it or its tubes to rest on other objects
i really feel the filters are not loud but best of luck solving your problem