Knocking sound, any advice? Thanks!

[cfan10]

The 350 TBI has devolved a tapping/knocking noise at idle, noticeable but not really loud. Checked oil it was a little low, added some went away for a little while. Knocking came back at stop light after maybe an hour. Also, my oil gauge on cluster is making a clicking noise and is always on the first line lately while driving sometimes after adding oil it moves to almost the center line but quickly goes back to the first line, it kind of vibrates while driving.
Could this be the engine going out? It seems to run really well and picks up speed with no issue. I usually only drive in overdrive to save gas not sure if that matters. Any advice is greatly appreciated thanks in advance for your time.

90 burb 350tbi unknown miles.