Why does different temperature water sound different

Qi did a program featuring this very subject.

Oooh really, I'll hunt that down

Surface tension and viscosity both reduce as water gets hotter - either could make it seem more “splashy” when poured.

Oooh really, I’ll hunt that down

Careful, if you pore over the details too heavily, you'll pour yourself inside out.

I haven't yet figured why water expands when it is solid or why clouds don't fall from the sky. Well they do when it's raining, obviously.

An old Tom Scott YouTube video:

I haven’t yet figured why water expands when it is solid

the quick answer is hydrogen bonding within the crystal structure of ice, this forms a particularly organised but actually relatively inefficient packing of the molecules.  Once there is enough heat to melt the ice, the molecules can move into configurations which are more disordered but more space efficient.

Air bubbles are larger in hot water so produce a lower pitched sound, apparently.

I haven’t yet figured why water expands when it is solid

Because the molecules have to form a crystal structure when the liquid becomes solid. Because of the nature of the bonds between the hydrogen and oxygen atoms, each hydrogen atom wants to be sandwiched between oxygen atoms. There are twice as many hydrogen atoms as oxygen atoms so there have to be gaps in the crystal structure. That crystal structure takes up more space than the molecules moving freely in a liquid state.

why clouds don’t fall from the sky

The sky actually falls away from the clouds. What you're seeing is an optical illusion caused by your frame of reference being grounded. If your frame of reference was in the clouds, it would be obvious.