loud knocking - just sharing

Thursday I noticed a loud knocking sound from the engine, it's a 99 with about 145k on it.
Got it dirt cheap a while back, didn't drive it much, had to return the rental so now it's now my DD.
I figured it was toast but went ahead and picked up new oil and some slick50 stuff hoping that would help. Wasn't ready to do the 2twisty.
Today I was warming up the engine to change the oil and was trying to figure out where the knocking was coming from, almost sounded like an exhaust pop but wasn't from the exhaust, couldn't figure it out. While standing over the engine frustrated I notice the back spark plug was moving with the knock, pushed on it and the sound changed. The darn sparkplug was loose!
Put in new plugs and it's running good again, still needs some work but at least it's not toast and I can still drive it!

Just sharing in case someone else runs across the same problem.
Never seen this problem but I always tightened spark plugs when I put them in.

My Dad bought a car when I was a kid (a long time ago) from a guy who thought the engine was bad. On the test drive, my Dad pulled over, popped the hood and found a spark plug wire that was loose. Pushed it on, drove back to the guys house and bought a very good car for cheep.