I can live with hold music even for an hour because I can keep it in the background.
The absolute WORST is when they play some music for 30 seconds, then the music stops, cutting to some voice recording peddling some bullshit like “try out [Product]!” or “Use our new mobile app!”. I can’t focus on anything else with it in the background because I think each time it cuts the CSR might have picked up the line.