I don't actually know how, but I often see people on Reddit talking about changing files to make Sonic, or any sound effect, much less ear-rapey. With a Sonic/Mental Blaster myself, I do agree that Sonic Attacks are not something I want to constantly listen to for extended periods; up there with Psychic Blast (and Fortuna psi attacks by extension) as well.
That said, Sonic/Mental is actually pretty sweet. The mix of Smash, Energy, and Psi damage is a solid amount of coverage. Psychic Scream is helpful to add an extra ranged cone (I personally see Sonic as one of the weakest in terms of raw damage output and lacking in AoE damage, so extra attacks are helpful) and Sonic's -Res help out with the frequent Psi resistances you run into late, plus Siren's Song pretty much guarantees Drain Psyche can be used without fear of death.
I have the same issue with Sonic, I can only play it for a limited time before it starts grating on my nerves. I have yet to come up with replacement sounds, though with my Therm/Sonic Def Tubthumper, all the steam whistle sounds seem appropriate.
There just happens to be a thread down in guides to solve your sfx issues. ^.^