If you hold it tense you get a rumble as described but the first time I tense it will make a little click. If I keep applying tension and release eventually it will stop clicking and just I'll just hear the rumble and it will take a bit to "reset" to where it clicks again.

Humans are weird.

Edit: I quick kagi search turns up a Reddit thread saying the clicking is caused by "Voluntary Opening of the Eustachian Tubes" which is equalizing the pressure in my ears. That sorta explains why it stops clicking after a bit.