Originally Posted by Skinjob
It's possible the Fuze is the problem, but I'd say it's unlikely unless you experience the same problems through the headphones. If you can't reproduce the problem over the headphones, then I'd say there's nothing wrong with the Fuze's output.
Do you have another device you could try, like a portable CD player? If so, connect it via the headphone output and see if you have the same problem.
It does not produce the same problem with regular headphones, just in some speakers I tried (And my car, even then it's about 5 years old now). But one thing I forgot to mention was that, the portable speakers I first tried were quite old.