Unusual keyboard operation

I'm using a dell precision m65 and I'm getting strange keyboard performance particular pressing the down arrow or delete key. Intermittently pressing one of these key types /n or b in word or minimizes the window or brings up the search window.b It does this in both windows programs and in Firefox. It appears to be quite random in nature and does not produce the same out come all the time. I've check the function alt ctrl shift tab etc keys for some weird hotkey combination but can find none. Any ideas?