Why is random text appearing when I'm trying to type?

Why is random text appearing when I'm trying to type?

the problem I am having, is that when I am trying to type something, text
will suddenly appear where I am typingall of the sudden,all of the
suddenall of the suddenall of the suddenall of the sudden(<-like that) (I
didn't plan that)
I have noticed that the text that appears is usually something I had
selected previously. It's as if I copy and pasted it, but I never copied
the original text, and never asked it to paste. It is very unpredictable,
often happening four or five times in a row, with less than a second
between each 'paste'. I am running in Linux Xubuntu, and I have a split
partition with Windows 7. The same problem happened when I was running
CentOS next to Windows. I completely removed it and later installed
Xubuntu in the same partition. The problem has never appeared in Windows.
I've looked all over google, and no one seems to have the same problem.
I've found a rare few that had rogue characters appearing, but they were
always specific characters happening at specific times. On my system, they
seem to pop up anywhere there's a box to type in. I guess an answer I'm
expecting is that I'll need to wipe clean my hard-drive and reinstall it
all again or just put up with the annoyance, but I'm rather interested as
to what would even cause something like this, and what sort of root issue
would be at play.