Why is my desktop wallpaper flash a gray screen on and off?

Marvin - Vintage model means ( I'm to d*mned lazy to study anything that's not making money for Apple today). UNACCEPTABLE!

At least give us a clue as to what year your machine was made. There are known issues. Please tell me just what a program like "CleanMy Mac" does. What did it remove? What did it change? Why would any sane person use something that does things you don't understand or have any idea of what it's doing. Do you have to wait till a class action law suit tells you this is BS like MacKeeper? Reinstall you system and get rid of the third party FIXs.

UPDATE 3/3/16

Thanks for the hint, here's your machine, I'll change the icon:

Apple iMac "Core 2 Duo" 2.66 20-Inch (Early 2008) Specs

Identifiers: Early 2008 - MB324LL/A - iMac8,1 - A1224 - 2210

Pre-Installed MacOS: X 10.5.2 (9C2028) Maximum MacOS: Current*

Details: *This system can run the current version of OS X 10.11 "El Capitan" as well as the last version of OS X 10.8 "Mountain Lion", OS X 10.9 "Mavericks", and OS X 10.10 "Yosemite" including booting in 64-bit mode. However, it does not support OpenCL nor does it support AirDrop, AirPlay Mirroring (which also requires a 2nd Gen or later Apple TV), Power Nap, or other advanced features, either.

I'd start off downloading and installing 10.10.5 from the Apple App Store or 10.11.3 so you can get the Repair Partition. Back up your user data first to an external HD with a system on it. Install the new system from the external drive. If you don't have an external drive, get one so you can repair and later use Time Machine to back up. You can migrate your user data later. You don't know what has been removed with Clean Your Mac so start over. I'd even reformat the drive and then install. After you have done this see if any of your issues persist and let us know. Sorry I'm very opinionated about these third party Mac Repair programs as I've only seen problems with them.