Can you figure out whats making the noise? I think it might be your HD -working to hard. One reason could be to a large and very segmented files. In Tbird and many other email clients, the most common reason for large files are keeping everything in one folder and never compacting. Remember that a folder are mail and attachment stacked one after another in a single file. (until compacting it also include all deleted ones!!) http://kb.mozillazine.org/Keep_it_working_-_Thunderbird