02 silverado knock sensor problem

I have an '02 silverado with the 4.8l engine and I am getting a P0332 code "knock sensor signal frequency outside normal range". I have cleared it several times but it comes back withing a few minutes. Does this mean the sensor is bad or is it telling me the engine is knocking? The sensor is under the intake manifold so it is a faily big job to replace it. What else should I look at? Thanks for any help.