Flickering mouse cursor/black bar on iMac 27"

I recently bought a refurb 27" iMac (mid-2010) and did a DIY upgrade to add a SSD in addition to the regular hard drive. I tested the system before cracking it open and everything seemed fine. After the install, I started noticing that the mouse cursor would flicker and sort of ghost itself and also that a small rectangular black bar would appear underneath the cursor. I can use it fine and it doesn't show up when I play games but it's driving me nuts. I know there was some kind of problem if you used an extra monitor but I'm not using one. I took a picture of the problem and can provide it on request. Any input would be appreciated.