It could be USB “drop out” where you momentarily lose connection between the controller and the PC.
I took this from the Serato forums with respect to MAC, but should give you a little more insight in to things to check the PC equivalents of.
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Am I getting USB dropouts?
If you’re getting audio glitches, clicks or dropouts, then there is a high chance you may be experiencing a USB dropout.
A USB dropout may be shown by the USB dropout indicator lighting in Scratch Live or ITCH, however this may not always happen.
What is a USB dropout?
Scratch Live and ITCH create what’s known as an isochronous stream of audio data over the USB bus. That is, it is ‘fed’ at precise intervals from our USB buffer. If for some reason what is in the buffer can not be fed onto the bus, the USB dropout indicator will light, and more often than not, you will hear an audible click or glitch in the audio. This is a USB dropout
Troubleshooting a USB dropout:
There are only a few things that can cause dropouts on a Mac. Here is a quick checklist to run through that helps cure most Mac USB dropouts:
1. Make sure your Airport is off.
2. Make sure your Bluetooth is off.
3. Make sure your Screen Saver is set to ‘never’ come on.
Go to System Preferences > Desktop & Screensaver
4. Uncheck ‘put hard disk to sleep when possible’.
Go to System Preferences > Energy Saver
5. Set your computer and display sleep settings to never.
Go to System Preferences > Energy Saver
