I recently bought a used guitar (a Sterling JP60) and I just noticed this problem - I am hearing a strange, irritating "flutter" like sound through my amp when a note is ringing out. Particularly obvious on the first two strings, and when the sustained note is after a pull off but also happens during bends and normal playing sometimes. Here is an example

<https://vocaroo.com/i/s1GX45TQkB61>

Any thoughts on what's causing this and how it can be fixed?