I would probably ask for clarification. I like being able to know what someone said. I would never assume he said, "I love you," in such a low tone of voice, thought I might wonder what he said if he did not clarify. That's just the way i see it though.
The Bloodhound Gang "The Roof is on Fire"
Live "All Over You"
Incubus "Talk Show on Mute"
Christina Aguilera "I Turn to You"
Bryan Adams "I Do It For You"
Uncle Cracker "In a Little While"
Korn "Hold On"