Why does PD generate noise?
The noise may be caused because pd is not able to keep up with the sound card. Regular buffer underruns sounds can sound like a steady tone. Try starting with a larger number of frags..., e.g.
pd -frags 15
If I buy a MOTU 828 (or some other interface) will that noise go away? If I use ASIO drivers instead of the standard drivers, will that noise go away?
No idea.
Good luck, andy