This happened to me when I was in high school, about 15 or 16. I was at my friend's place on Number One Pond. She lived in an apartment that had caged compartments in the basement for the tenants to use as storage. It was late at night and I had never been to her house before.
We were in the basement talking and hanging out as her parents were asleep. We were laughing and joking around when I heard what sounded like a male voice whispering loudly. I looked around the basement and realized that we were alone. She didn't seem to notice, so I figured I'd forget about it. About a second later, though, she stopped talking and said, "Did you hear that?"
I was frightened because her question confirmed what I thought I'd heard. I told her that I had heard it as well. We both freaked out and ran up the stairs outside. I decided to go home since we couldn't hang out in her actual apartment, and no way were we going back in the basement.
I can't really describe what I actually heard. I know it was a male voice, and it was a loud whisper that filled the entire room. I couldn't make out what - if anything - it was saying. I wasn't paying attention because I hadn't expected it. To me, though, it didn't sound like he was saying anything. It just sounded like "aaaaahhhh rrraaaaaahhhh." My friend's name is Ashley, but she does have a sister named "Sarah." And "Sarah" is also a very common name, so maybe that's what he was trying to say.
To my knowledge, there were no other experiences in the basement. Ashley and I talked about the incident a couple of times since, but we've lost contact. She never told me about anything else happening in the apartment before or after that night.