Can one leave an alarm to go off on Shabbos morning?
If one can, then can it play anything, music, radio, etc?
I learned that the prohibition of generating sound on Shabbos even through a trigger - which is plainly permitted in general - was related to the prohibition of musical instruments on Shabbos. R'Eli Mansour brings the reason that it's not in the spirit of Shabbos to watch television or listen to the radio, and specifically prohibits using an alarm that turns on news or music.
Some rabbis prohibit waking up to music period, although the question would be whether or not recorded music qualifies as actual music in this regard, as the Shulchan Aruch is regarding "musical instruments". Furthermore, this may be informed by the general prohibition to listen to music at all.
It's interesting to see R' Auerbach Z"L ruling this way as he generally seems to hold that we cannot say that specific laws such as this apply to modern inventions. He is presumably understanding the speaker which produces the music to be a resonant body as one would find in an instrument, its electrical component notwithstanding.