Learn English – Name of the high pitch sound produced when objects are hit against each other underwater

Right from when the water first starts to suck air into the eddy going down a plug-hole, the sound it makes is gurgling - defined by OED as the noise made by liquid escaping intermittently from a vessel.

Personally, I call the sound made at the very end a glug (OED: a word formed to imitate an inarticulate sound).

Glug functions as a verb, as well as a noun. Obviously, if water glugs, that just means the water is making that sound. But in another common usage, to glug means to drink (often, the last drops of) something noisily and/or hastily - glug the last dregs in a glass of beer, for example.

Regarding “would you call [Dad or Mum] a name?”, I think a term like cognomen or sobriquet is more appropriate than appellation or name.

• cognomen, “a nickname or epithet by which someone is identified; a byname; a moniker or sobriquet”
• sobriquet, “A familiar name for a person (typically a shortened version of a person’s given name)”

Note, while epithet has a well-known sense (“An abusive or contemptuous word or phrase”) with negative connotation, that is not the sense used in the definition above of cognomen. Instead, the relevant sense is “A term used to characterize a person or thing” or “A term used as a descriptive substitute for the name or title of a person” (in which sense epithet also can serve as an answer to the original question).