Why does boiling water have a lower splashy sound compared to cold water when it is being poured?

During study leave for my AS exams, I have made myself plenty of cups of tea. Something that caught my attention and made me curious was that when you pour boiling water for a cup of tea into a mug, the splashing sound that is created is lower in pitch than if you were to pour cold water.

After typing this question into Google, I did not manage to find a conclusive answer to this conundrum, so I decided to do some research myself. Here a series of questions that I asked myself when trying to work out the reason behind the different splashy sounds.

Why are we hearing a splashy sound in the first place?
I did a quick Google search and found this article by NASA's Earth Observatory: How do Raindrops Make Sound Underwater? The sound generated when a splash of water being poured into a mug is pretty much the same sort of idea as when a raindrop hits a puddle so this article was very useful. The article states that "there are two components to the sound generated by a raindrop splash:  the splat (impact) of the drop onto the water surface and then the subsequent formation of a bubble under water during the splash".

What causes variation in pitch?
The pitch of a sound depends on the frequency of the vibration that causes the sound. Therefore, the higher the frequency, the higher pitched the sound emitted. Also in this particle, they also mentioned the Minnaert Resonance, the acoustic resonance frequency of a single bubble in an infinite domain of water. Obviously the water already in my mug is not an infinite domain of water, but if we ignore the effects of the mug, I reckon Minnaert's equation can still be used. It stated that the frequency of the sound emitted depends on bubble radius, local pressure, local water density and a geophysical constant.

Which one of these variables is causing the variation in pitch? 

• Bubble Radius

From my initial observations, I did not think there was any variation in bubble radius with changing temperature. However, then I thought about it a bit more and realised that water is more "runny" when it is hotter. In more scientific terms, water has a lower viscosity at higher temperatures, due to less hydrogen bonding. Therefore I concluded that at higher temperatures, the bubble radius must be smaller - is this a correct assumption to make?

• Local Pressure

I was mostly pouring the water into my mugs of tea at the same spot in the kitchen so there was probably no significant change in local pressure in the ambient space. Pressure, therefore, becomes a constant.

• Local water density

Water density decreases as temperature increases, so with hotter water, there is a lower local water temperature.

What is my conclusion?
As temperature increases, the bubble radius decreases as it has a lower viscosity. However, local water density decreases as temperature increases, which is not any use as both decreases will cancel each other out algebraically. Perhaps I need to consider the constants or maybe bubble radius decreases less than the decrease in density, so the decrease in density is more significant? In conclusion, I haven't really come to a conclusion! I will continue pondering about this conundrum in the morning and will report back when I have found a decisive conclusion!