Knock Sensor records at 4000 rpm, in drive

2005 Mazda SP23

2005 Mazda SP23

Has anyone used Mazda OBD Software and tested the knock sensor in drive at higher rpms?

I have a situation that my Knock sensor trips at 4000 and the timing, of course, retards to adjust. I have checked, spark plugs coils, motor mounts, loose objects banging against block, PCM s/w current, carbon build up is clear...Mazda dealer says they can't find anything. I use 89 octane. The airbox resonator is taken off but no other mods to the engine.

Appreciate the help.