org-agenda-log-mode-add-notes

org-agenda-log-mode-add-notes is a variable defined in `org-agenda.el'.
Its value is

t

Documentation:
Non-nil means add first line of notes to log entries in agenda views.
If a log item like a state change or a clock entry is associated with
notes, the first line of these notes will be added to the entry in the
agenda display.

You can customize this variable.