One problem related to engine knocking noise has been reported for the 2006 Infiniti M35. The most recently reported issues are listed below.
Took car to Infiniti of santa monica, CA for routine 30,000 mile service. They returned car to me with a ticking/ knocking noise coming from engine. They told me it was from the fuel injector cleaner they added to my car. Took car back to them 3 times in one day and finally refused to leave until they repaired it. They say I need a new engine due to a manufacture defect. I never heard the knock in 30,000 miles, I never heard the knock until I drove out of Infiniti of santa monica, CA. Car only has 30,000 miles on it.