mouth music

noun3

1. •
   The vocal imitation of instrumental music.

   • She herself or one of the other crofter women of the townland would sing to us the mouth music. — 1877
2. •
   (slang) Oral sex.

   • At some point in almost every gay encounter someone will play a little mouth music. — 1977
3. •
   Words (or sometimes actions) that sound good but do not mean anything.

   • I lived both with no belief in a higher power and I lived with a so-called religious belief in a higher power that was purely a dead religion. It was just mouth music. — 1982