My iMac has a life of its own !?...

hello to all
in the last few days something most disconcerting has been happening on my iMac : when i'm typing something ( regardless if using Mail, TextEdit, filling out a ''box'' or other.. ) suddenly it starts typing capital i's endlessly, like this : IIIIIIIIIIIIIIIIIIIIIIIIII - luckily in ''short'' 15 to 20 letter bursts, except twice where it kept doing it until i restarted it.
first, even though it's a new keyboard that has NEVER had a drink spilled over it, i thought a key was sticking so i removed the batteries from my wireless keyboard &.....it kept typing alone thus ruling out the keyboard as the source of ...
i don't know if related but a few days before it did twice a burst of alert sounds ( i have funk selected.. ) that sounded like a ''machine gun'' effect made of said funk alert sound
so far i've only had three or four episodes but i'm dreading this could become more serious - as in permanent..
anyone has a clue what this is ? is this a symptom something nastier is about to happen ? should i stop using the iMac until this is sorted? any help will be greatly appreciated
thanks
Nuno

of its own!?...

to make sure Snow Leopard wouldn't give me any undue grief , i did a fresh, clean re-install of OS X, then Snow Leopard & the few softwares i have. i have every software update, got fresh batteries for the keyboard & mouse, re-paired them with the computer...
the thing that freaks me a little is that after removing the batteries from the keyboard , IIIIIIII's where still being ''typed'' as if the keyboard still had batteries & i didn't lift my finger from the ''I'' key, weird....
Nuno