Hello, I wish I could tell you 100% what the problem is but a scanner needs to be hooked up to fully test the knock snsor and signals sent. I included the diag flowchart, wiring daigram as well as explanation in an effort to try and help. It is very possible there is an internal noise developing after hot and when oil is hot and thin that the sensor is detecting even if you can not hear the internal noise. they are fairly sensitive
Electronic spark control is accomplished with a module that sends a voltage signal to the ECM. As the knock sensor detects engine knock, the voltage from the ESC module to the ECM drops, and this signals the ECM to retard timing. The ECM will retard the timing when knock is detected and RPM is above about 900 RPM.Code 43 means the ECM has been low voltage at CKT 485 terminal "B7" for longer than 5 seconds with the engine running or the system has failed the functional check.This system performs a functional check once per start-up to check the ESC system. To perform this test, the ECM will advance the spark when coolant is above 95~C and at a high load condition (near W.O.T.). The ECM then checks the signal at "B7" to see if a knock is detected. The functional check is performed once per start-up and if knock is detected when coolant is below 95~C (194~F), the test has passed and the functional check will not be run. If the functional check fails, the "Service Engine Soon" light will remain "ON" until ignition is turned "OFF" or until a knock signal is detected.
Code 43 can be caused by a faulty connection at the knock sensor at the ESC module or at the ECM, Also check CKT 485 for possible open or short to ground.See Diagnosis By Symptoms - No Trouble Codes Stored.