Engine knocking noise

The car only had that knocking sound one night while warming up. Then it stopped. It has not done it before nor since. There is a leak, though, that looks like antifreeze. I hope that is it! What is a mystery to me is that the radiator is full as well as the antifreeze/coolant overflow container. It is with a mechanic that I know and trust now. I will upload a video for you to see.

Thanks, Ken. I just got the car back from the mechanic. It had three leaks coolant. The hoses were good, so he replaced all the clamps because two were loose. I am interested in your reason for suggesting I use a heavier weight oil. What does that mean, and what is the reason you think I need to change oils? Thank you. P.S. Yes, I have found that instead of trying to describe noises or issues videos or pictures work wonders in helping a mechanic troubleshoot possible problems. Invariably, the noise or issue someone tries to explain is difficult at best. Are we not thankful for Smart phones? Lol

There was only a knock that one night--never before, never since. I don't know what the deal was. The noise could possibly have been that piece of plastic underneath the front of the car which was loose and now is tightened back. After replacing the hoses, the plugs, all fluids, and a PS senor last summer, I have learned that old adage "If it ain't broke, don't fix it" to be true. Until I had all that done as maintenance because there were no problems, nothing at all was wrong with this car. With motors, if nothing is wrong, it seems to me --unskilled though I am-- that if nothing is wrong, leave it alone. When things begin to get moved around etc. On a ten-year-old motor, it seems that it affects other things. For now, I think I will stay with the same weight. This mechanic did an engine pressure test of some sort and told me this car should last for a long time. He also checked stuff about the motor. I feel safer in it now than I did knowing he truly gave it a good going over. Thank you for all your help. It is wonderful that you are here online to help, especially women who know little to nothing about these things. Believe me, I have been "had" when it comes to mechanics, which is the reason so many are not trusted. I surely don't know of any such as yourself who gives of his own time to try to help. Thank you.