1989 chevy c1500 knock code

Sounds like the knock sensor or knock sensor module is bad. The ECM will run a diagnostic test on the knock sensor circuit buy advancing the ignition timing to the point that the engine should knock and the ECM should receive a signal from the knock sensor. This diagnostic test is run with the engine fully warmed up and under acceleration, usually heavy acceleration like merging into expressway traffic. What you're hearing is the engine knocking while the test is being run because the ECM is not getting the signal from the knock sensor. If the ECM was getting the signal from the knock sensor the test would run so quickly you wouldn't notice it. Hope that helps! Jim