How many miles on the motor? What bolt ons do you have.
I had this same issue when I went FI the first time. I ended up tuning it myself and pretty much eliminating all the knock by just pulling timing from the BKT.
I as well never felt or heard any knock until I tapped into the knock sensor from the ecu harness and listened through my stereo.
Wish i could help you. It's a crappy thing to deal with.