Audio playback stutters when downloading - what's problem?

I'm on WM10 but am fairly sure this is a general problem as it happens in
application based playback online as well.

The first time i noticed it was watching a music video online - the music
would stutter continuously until the whole song was buffered and then it
would be ok after that.

Just now i was downloading a rather big game patch and my windows media
player was stuttering while the downloading was taking place. When it
finished it was fine.

Thinking about things i expect if i were to tell you now that it isnt a
problem with system resources as i have checked that - i can play music while
playing on resource hog games - so it must be something messing up on
download.

Can anyone help?