Newbie here too. I’ll try to help out. I’ll assume you know how to use Asset Manager. If not, here’s a guide [Script][Basics]Modding Beginner's Guide I. You don’t need to know alot, just follow it and I’ll try to explain what to do AFTER you have it ready to use.
Don’t know if there’s an easier way, but what I would do would be:
In Asset Manager, go into records\sounds\items\weaponattacks.
You’ll see alot of spak_something.dbr. Before going any further, you have to understand one thing: Weapon sounds and projectile/impact sounds are 2 different things.
So you should be sure of which sound you don’t like hearing.
Is it the firing sound or the enemy being hit sound ?
If it’s the firing sounds:
The sounds for guns shots are named spak_X_shot.dbr. For example: spak_rifle_shot.dbr
Open any of these, go into Sounds Properties, and you should see:
soundName1 using sound\items\weaponattacks\rifle_shot_01_mono.wav
soundName2 using sound\items\weaponattacks\rifle_shot_02_mono.wav
soundName3 using sound\items\weaponattacks\rifle_shot_03_mono.wav
soundName4 using sound\items\weaponattacks\rifle_shot_04_mono.wav
Just change rifle_shot_X_mono.wav to crossbow_shot_X_mono.wav (it goes up to 04). This makes it so all firing sounds of any RIFLE instead play the crossbow sounds. Also, if you scroll down a bit, you’ll see weightX with the value of 25 up until weight4. This controls the chance of hearing each sound (1 out of 4 times you’ll hear rifle_shot_X_mono.wav, essentially looping through them).
If you favor one specific sound, just adjust the values, giving an higher value to the preferred sound. CAREFUL: they should add up to 100, so don’t make something like: 75, 20, 10, 10. = 115 or something less than 100. I don’t actually know if this can break the game in any way, but I wouldn’t try it. Especially 100+, since <100 probably results in sometimes having a firing animation with no sound. 
Anyways, if instead you don’t like the enemy being hit sound:
The process is basically the same, instead of editing spak_X_shot.dbr, you’ll edit spak_bullet_X.dbr and change the sounds to what you want.
Notes:
If you wanna preview the sounds, Grim Dawn\resources\sound\items\weaponattacks and use Windows Media Player or any other program to open the .wav files.
Keep in mind you should be able to change the sounds into different weapon type sounds.
Also, spak_thunderclap_shot.dbr is actually a skillsound called doom_bolt_cast.wav, and is instead located in Grim Dawn\resources\sound\skillsounds\class03. Thunderclap refers to the Epic Two-Handed Ranged weapon with the same name. https://www.grimtools.com/db/items/2475
As you can see, it’s not hard, but a little bit annoying going through and picking the preferred sounds. I apologize on not explaining how to use Asset Manager, but the link I give should point you in the right direction. 
Also, I’m not anywhere near experienced with modding. Learning it as I go. 