Desktop icons are flashing and refreshing periodically on my iMac

All of a sudden, the desktop icons on your 27 inch iMac start flickering almost every minute. To resolve this issue, apply those few steps:

1. Back up all data.

2. Uninstall Google Drive according to the developer's instructions.

3. Uninstall SIMBL as follows.

4. Select Go ▹ Go to Folder… from the Finder menu bar, then enter the following text in the box that opens:

 /Library

5. A folder will open. From that folder, delete the items listed below (some may be absent.) You may be prompted for your administrator login password.

Application Support/SIMBL

InputManagers/SIMBL.bundle

LaunchAgents/net.culater.SIMBL.Agent.plist

ScriptingAdditions/SIMBL.osax

6. Log out and log back in.

Note: Make sure you never reinstall SIMBL. It’s likely to come bundled with another third-party system modfication that depends on it. If you want trouble-free computing, avoid software that makes miraculous changes to other software, especially built-in applications. The only real exception to that rule is Safari extensions, which are mostly safe, and are easy to get rid of when they don’t work. SIMBL and its dependents are not Safari extensions.