I'm having the same problem discussed here a couple years ago:
http://thread.gmane.org/gmane.editors.textmate.general/20093
On my dual g5 powermac (leopard 10.5.6) I get the alert bell whenever textmate (r1496) loses focus and the "save file when focus is lost" option is enabled. I couldn't find any debug info anywhere. It happens even if I create a new file from the command line this way: $ mate foobar.txt The file is written with no problems. This doesn't happen on my macbook. Thanks for any info... Cheers