Put the bike on the centre stand and have a look at each chain link. When they stick or rust they tend to position at an angle rather than horizontally so fairly easy to spot.
Once they sieze up there’s little chance of it being good again, even with a bit of manipulation and cleaning/lubing.
The knocking on the footpeg tells me you will find some links at an angle, so time for a new chain & sprocket kit.
D.I.D. X Ring is what i stick to as well, as long as you keep them lubed, with the occasional clean they’ll last a long time. Saying that, if you neglect any chain then they will fail on you sooner rather than later even from new.
No need to buy the ‘extra’ heavy duty version though.