my 06 has begun intermittently making a 'chk' sound and a slight jerk. No cel. none pending. I pulled the mah connector to frce a CEL so I could look at freezeframe data. fuel trims looked OK.
I only have 45K miles but changed the (original) plugs anyway (they looked good)
still have the problem.
I think I will inspect the CA sensor as suggested here. If I see any debris, I'll take pictures.