Background music doesn't stop when jukebox plays a disc

Description
When a music disc is inserted into a jukebox while the game's ambient background music (biome‑specific or menu‑style music) is already playing, the background music does not fade out or stop. Instead, both the background track and the disc track play simultaneously, causing audible overlap and distortion.

Expected behavior
The background music should stop (or fade out) immediately upon disc insertion, leaving only the disc's music audible.

Actual behavior
Both audio streams play together, with no interruption to the background music.

Steps to reproduce

1. Enter any world (Survival or Creative) with the "Music" volume set above 0 in options.

2. Wait for the ambient background music to start playing (typically shortly after entering the world or when entering a biome with its own music).

3. Place a jukebox.

4. Right‑click the jukebox with any music disc in hand to insert and play it.

5. Listen to the audio output.

Observed result
The background music continues without any change, and the disc music is layered on top of it.

Expected result
The background music stops or fades out, and only the disc music is heard.

Additional notes

• This issue is specifically about ambient background music overlapping with a jukebox disc, not about two discs overlapping (which is a different known issue).

• I have searched Mojira and did not find an exact match for this specific behavior. Please double‑check before submitting.

• Tested in a clean, unmodded environment to rule out conflicts.