For that matter - some cell phones do strange things to your room audio too. Not all people hear the high frequency noise - but the ones that do hear it - I understand, it can be rather bothersome. It very well could be - like you said - a wireless device coming into the classroom or the florescent lights. That's my vote.
Good luck Steve! If you do find what the cause is - please let us know! Thanks.
Best regards,
Emily Trapp
Director, IMS
SUNY New Paltz
1 Hawk Drive
LC 2B
New Paltz, New York 12561
(845) 257-3634 - Voice
(845) 257-3646 - Fax
www.newpaltz.edu/ims
www.stc.suny.edu
"Engagement will become the central issue for education in the future and learning won't necessarily be defined by how much 'seat time' a student has put in." Stoloff