Why would my car have engine knock for the first time after and oil change?

If the knock senor was disturbed when the oil change was performed...First check I would do...visually confirm its not broken or unplugged. located near the oil filter.

Low oil level. Check to make sure they put oil in the engine.

Thank You! I did check to see if there was oil. It was a new Mechanic and I wondered if he put in the wrong oil. I will check the knock sensor!

maybe some idiot at the shop fired it up before putting the oil back in .