Feasible Audio Project.

My friends and I are always pranking one another. I was the last one to be pranked so it is my turn to return the favor.
My target is somewhat of a fraidy cat. With this in mind I was talking with my brother about how it would be really funny if I could somehow have some spooky sounds play at random times. I was thinking about using my laptop but my brother told me about Arduino. I've looked at some stuff about arduino on youtube and on a few websites and it looks like it could be what I need but I am not sure.
My question is this. Can I make something that will play a random mp3 every 5 to 30 minutes and play the sound through 1 to 3 speakers?
If it is possible what do I need? Do I have to have a mp3 shield for this to work?

Can I make something that will play a random mp3 every 5 to 30 minutes and play the sound through 1 to 3 speakers?

Yes. An Arduino with an Adafruit wave shield can play .wav files in this way. You will have to have some sort of switching arrangement to switch to each speaker though.

How about spooking him with a knocking noise. A simple solenoid or two under the floorboards would give a very Edgar Allan Poe vibe, and it is a lot cheaper than a wave shield.