This may not be trinity related, but I don't recall thunderbird making
this noise in MATE.. When I am reading emails, and hit "n" for Next, and
NExt takes me to a new folder ( not every message, just new folders) it
makes a harp-like sound trill up then Down.. any idea what setting that is??

-- 
Paul Cartwright
Registered Linux User #367800 and new counter #561587