Code P0324 knock sensor

I have received this code 3 times, 2 times it came on after driving 40 minutes and turned it off for maybe 5 minutes, upon startup the check engine light came on. I don't remember how the other one came on.
I changed the spark plugs and cobs, spark plugs weren't tightened properly. The light still came on. I read some posts that there are two bolts on top of the timing chain area that might be loose. I wonder if this might be the problem or any other suggestions. I also took the dipstick out while running and have vacuum at least that what somebody's post stated.