fuck it, i'm gonna dump one of my cdrw headcanons here. if y'all like this, i'll share more ¯\_(ツ)_/¯
so. unless removed. cybertronians generally have a voice modulator, which is responsible for producing the vast majority of sounds that make up spoken cybertronian. however, there are certain tones that can add certain inflections or meaning to other words, that aren't produced with the voice box, but by moving other body parts to create other sounds. spinning wheels, revving engines, as well as innumerable other more subtle noises can be used to accent words and emphasize the speaker's opinion.
the general way that the tones work is that certain sounds in spoken cybertronian are paired up with different types of noises to mean different things. combinations of noises that sound pleasant to the ear generally have positive connotations, while harsh noises have more negative ones. some tones are produced using fairly universal parts, and are thus widely understood, and others are more up to creative interpretation of trying to figure out what internal mechanisms you have that make a sound closest to the accepted tone, and generally it takes time to get to know someone before you can understand and contextualize all the tones they're using.
you can be very overt about what you're saying, and, for instance, make it incredibly obvious that you're talking to the love of your life just by the way that you say their name, or you can be more subtle, and call your boss a dipshit to his face without him noticing.
so we know. from canon. that when chromedome is having nightmares that sometimes he says names in his sleep. and. it is my personal headcanon. that rewind has known about mach, pivot, and scattergun for almost as long as he's known chromedome.
so rewind kind of expected to hear their names at least every now and then, thinking that maybe chromedome's subconscious mind would remember them even if he didn't.
but he never did. and eventually he just assumed that maybe they were really gone for good in chromedome's mind.
then one day, he started noticing chromedome making this weird noise in his sleep. just a strange pattern of mechanical noises. which can often be a sign of injury or illness, so he recorded the sound and they went and got it checked out. and it didn't seem like anything was wrong, so chromedome just kind of forgot about it.
but it kept happening, and rewind kept listening to the recording he had made.
until one day, just randomly, he happened to be thinking about chromedome's previous conjunxes, and their names. and it just suddenly clicks that the sounds chromedome was making would line up perfectly for very affectionate tones for their names, ones that imply the speaker was talking specifically about their conjunx.