WHAT WOULD CAUSE A KNOCKING SOUND (LIKE A KNOCKING ON A DOOR SOUND)?

No. As a matter of fact, when it started it was only when I first started the car. Eventually I would hear it on & off while driving as well.

That means a technician can hear it in the service bay which is a good thing - the best route to take is to have an experienced tech check this out for you.. This will likely involve leaving vehicle at the repair facility for awhile.. There’s simply too many possibilities for online diagnosis. Good luck!

Ok, thank you pushrod for your help. I appreciate it.