Sound volume drops after repetition

I have a simple implementation, player jumps and it plays the jump sound. But the volume randomly drops. Weirdly enough, if I call the sound twice this doesn’t happen.

Here’s all the related code for sounds:

Mix_OpenAudio(44100, MIX_DEFAULT_FORMAT, 2, 1024) < 0)
Mix_Volume(-1, 0.1 * MIX_MAX_VOLUME);
void GAppMain::play_sounds()
    if (mPlayJumpSound) {

        /// this solution (sending jump sound to two channels) is ugly but it seems to work; find a better one
        Mix_PlayChannel( 1, GData::Assets::GR_Sounds.back().mData, 0 );
        Mix_PlayChannel( 2, GData::Assets::GR_Sounds.back().mData, 0 );

Even if I let if be -1 (to let SDL choose the channel) but call only once like this

Mix_PlayChannel( -1, GData::Assets::GR_Sounds.back().mData, 0 );

The volume drops, comes back, drops.

Any ideas?

Kinda let down the lack of engagement in these forums … I solved that problem by not using the volume at all, which isn’t really a solution but to play around for now it won’t hurt