There are speaker boxes inside most notebook machines which are far more powerful than those within earbuds or cell phones. Many people put additional speakers around their machine to have better (or at least louder) sound output.
The rumours that you could destroy floppies when you accidentally put them onto your speaker boxes seem to linger still. ;-) Don't worry, though. Unless you expose your machine to serious magnetism (anything that would visibly distort a CRT display from across the room or worse) you'll be fine. The notebook's chassis and the drive's case will shield off quite a lot, and the platter materials are far better today than they were in the past.
Just don't worry, for any possible everyday use you'll be safe.