噗通 PK 扑通: What's The Difference? If Any?
The way I see it is that 噗通 is neutrally describing the &quot;plonk&quot; sound when you drop something into a liquid, while 扑通 describes something going &quot;plonk&quot; into a liquid (there are other uses of these characters to describe other sounds). Generally, one is an action, the other is a sound.
Because the 2nd one is an action of &quot;going plonk&quot; (to phrase it inelegantly), it could be used comically to describe somebody falling into a pond, for instance. But, I wouldn't say that it's usage is connected to something being comical all or even most of the time.
Contrary to what one of your sources says, 噗 and 扑 are not variants of each other, and 扑 is not the simplified form of 噗 (it's the simplified form of 撲). It just so happens that the two are interchangeable in this one word.
Even though this difference exists, most people seem not to distinguish between them because they sound the same and are so similar in meaning. Many people will just use 扑通 all the time, especially on a computer when sifting through 扑通 and 噗通 is a pain.
To back up my claim with google:

扑通: 969,000 results
噗通: 639,000 results (and most of them a K-drama)
噗嗵: 74,000 results