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We have a DELL Latitude D620 as one of our 3 Home DELL Notebook PCs. I do know the StickyKey sound you are talking about bec sometimes I get it on my DELL Inspiron E1505/6400 as well.
Sometimes it will go away from itself and if it doesn't I will normally save everything and reboot, and it will be gone!
Normally our 2 kids use a 3rd DELL Notebook PC, older DELL Latitude D800 and I don't ever recall the D800 STICKY Keys, but I will tell you from having personally replaced an entire DELL keyboard on the E1505/6400 it is one solid piece.
Also if you want to troubleshoot the keyboard more on your own while waiting for DELL Technical Services, you might want to run the very comprehensive DELL DIAGNOSTICS that should already be preloaded...Otherwise you will find it on the DELL RESOURCE CD.
Hope the Above Info Helps and Best of Luck!