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What causes these radiator sounds?

I'd love to come up with an exhaustive list of the possible causes of the following sounds I've recently started hearing throughout my home. #1 (a and b) is coming from the air vents on the roads and mains. #2 is coming from most of the radiators as they heat up and then as they cool down when boiler shuts off, and is a metal pinging sound. Pretty sure it's expansion of the radiator itself (as opposed to feet on the wood, so milk jug trick won't work) but not sure what, if anything, to do about it. wondering if it could also be water hammer but don't think so.

The radiators are all cast iron (including the frame, which fills with steam) recessed radiators that are heavily painted over. Both of these noises did not exist or were very rare until a couple months ago following a leaky valve replacement, and both noises are happening with most if not all of my radiators, even when heating up only a degree (no setback).

I would like to start with a broad list of all possible causes given this information and narrow down from there. Thanks!
(I've also included pics of the rads for background)

#1: a) https://m.youtube.com/watch?v=75epDyvMjfM

b) https://m.youtube.com/watch?v=gC9cFno7ZuM

#2: https://m.youtube.com/watch?v=eumzFrS7DE4