This can happen on either PC or Mac.
1. If a digital connection is present, make sure the necessary Master and Slave clocks are set correctly.
2. Increase the Disk Block Buffer size in Cubase VST in the Audio System Setup.
3. Increase the buffers in the Sound cards ASIO setup utility.
4. If USB is not being used, disable it as it is known to slow down audio through PCI sound cards.
5. Defragment hard drives and check for errors.
6. Try switching from the dedicated ASIO device to the ASIO Multimedia driver if on a PC or the Apple Sound Manager on a Mac. If the pops and clicks go away when using these drivers, there may be a corrupt ASIO driver that needs to be replaced by newer drivers.
7. Check for Irq conflicts
8. Reduce Graphic acceleration
9. Reduce the number of running background applications
10. Update Sound Card Drivers
11. Move the Pci audio card further away from the video card.