Shoutbox

The most likely cause is that he/she has the mic to close to the mouth (often happens with so called head-sets).

It's also possible that, in addition, his/her mic's tone settings are a bit off, or not properly set for the mic he/she is using (eg: for a head-set, and a lot of other cheap mics, you should turn the bass a bit down and treble up).

And ask to articulate better, that's also highly important when speaking thru a mic (especially cheap mics for computer use).

Using a mic in the proper way is actually not so easy though. Singers, speakers, etc must build up some experience and often get lessons in how to handle a mic and how to properly speak/sing thru it (together with using good mics of course). It is not something which everybody can do properly, even after training.

If you also notice the same muffled sound while playing other sounds or music, then your own settings are a bit off.

To tweak the tone settings you need to go to your sound card's preferences panel. You can often access it thru the configuration panel of Windows.