I had the same problem with my 04 Silverado. But I had just tweaked the system and engine till it was getting
17.5 MPG. At that point, I researched carefully whether it was worth it to rip my engine, which was running like
a top, apart. I decided not to take the risk of creating more problems than it would solve. The knock sensors
don't do much after the first 20K or so, anyway. So I decided to leave them alone. STILL getting 17.5 MPG,
10 years later.

So ignore it. It won't go away.