[Dragokas]

I managed to found sound path and possible reason, but I was unsuccessful in attempt to fix it without using hook.

Your culprit is:

#define SOUND_THROWN_MISSILE 		"player/tank/attack/thrown_missile_loop_1.wav"

I didn't touch your plugin. Instead I cracked panxiaohai's.
When he destroys rock's entity, game engine does not stop automatically the sound of rock thrown.

RemoveEdict(ent);

Interception show:

L 12/16/2018 - 16:16:11: [l4d_tankhelper_hook.smx] player/tank/attack/thrown_missile_loop_1.wav L 12/16/2018 - 16:16:11: [l4d_tankhelper_hook.smx] numClients: 5, entity: 1, channel: 0, volume: 0.000000, level: 0, pitch: 100, flags: 4, soundEntry: , seed: 0 L 12/16/2018 - 16:16:11: [l4d_tankhelper_hook.smx] numClients: 5, entity: 1, channel: 1, volume: 0.000000, level: 0, pitch: 100, flags: 4, soundEntry: , seed: 0 L 12/16/2018 - 16:16:11: [l4d_tankhelper_hook.smx] numClients: 5, entity: 1, channel: 2, volume: 0.000000, level: 0, pitch: 100, flags: 4, soundEntry: , seed: 0 L 12/16/2018 - 16:16:11: [l4d_tankhelper_hook.smx] numClients: 5, entity: 1, channel: 3, volume: 0.000000, level: 0, pitch: 100, flags: 4, soundEntry: , seed: 0 L 12/16/2018 - 16:16:11: [l4d_tankhelper_hook.smx] numClients: 5, entity: 1, channel: 4, volume: 0.000000, level: 0, pitch: 100, flags: 4, soundEntry: , seed: 0 L 12/16/2018 - 16:16:11: [l4d_tankhelper_hook.smx] numClients: 5, entity: 1, channel: 5, volume: 0.000000, level: 0, pitch: 100, flags: 4, soundEntry: , seed: 0 L 12/16/2018 - 16:16:11: [l4d_tankhelper_hook.smx] numClients: 5, entity: 1, channel: 6, volume: 0.000000, level: 0, pitch: 100, flags: 4, soundEntry: , seed: 0 L 12/16/2018 - 16:16:11: [l4d_tankhelper_hook.smx] numClients: 5, entity: 1, channel: 7, volume: 0.000000, level: 0, pitch: 100, flags: 4, soundEntry: , seed: 0 L 12/16/2018 - 16:16:11: [l4d_tankhelper_hook.smx] numClients: 5, entity: 1, channel: 135, volume: 0.000000, level: 0, pitch: 100, flags: 4, soundEntry: , seed: 0

I tried:

PHP Code:

public Action:Timer_StopSoundDelayed(Handle:timer, any:thetank)
{

    // method 1
    // not work
    
    for (int i = 1; i <= MaxClients; i++)
    {
        if (IsClientInGame(i)) //&& GetClientTeam(i) == 2)
        {
            for (int channel = 0; channel <= 7; channel++)
            {
                StopSound(i, channel, SOUND_THROWN_MISSILE);
            }
            StopSound(i, SNDCHAN_USER_BASE, SOUND_THROWN_MISSILE); // 135
        }
    }
    
    // method 2
    // not work
    //EmitSoundToAll(SOUND_THROWN_MISSILE, _, _, _, SND_STOPLOOPING, _, _, _, _, _, _, _); 
} 


as well as a delay (3 sec.) before stop, but without success.

As expected, sound blocked ok using:

public Action OnNormalSoundPlay(int clients[MAXPLAYERS], int &numClients,
		char sample[PLATFORM_MAX_PATH], int &entity, int &channel, float &volume, int &level,
		int &pitch, int &flags, char soundEntry[PLATFORM_MAX_PATH], int &seed)
{
	if (StrEqual(sample, SOUND_THROWN_MISSILE, false)) {
		numClients = 0;
		return Plugin_Changed;
	}
	return Plugin_Continue;
}

If you want to continue experiment, here is a plugin with those several methods.
As for me, I prefer to block that sound forever, if another methods will be unsuccess.