That isn't a correct diagnosis; people have heard of aahed. You'll find it naturally in the expression "[someone] oohed and aahed".
People don't want aahed, and their instinct that it shouldn't count is reasonable, but unfamiliarity isn't the problem with it.
You can spell the sound "ah" however you like: ah, ahh, aah, aahh, there's no wrong way to spell it.
If you write "the washing machine tringged when it finished", 'tring' is not a word, even though it's following the rules of English morphology, you could have written any sequence of letters that most faithfully reproduces the sound of the washing machine. You could have written katrigged or puh-tringged.
https://www.oed.com/search/dictionary/?scope=Entries&q=ooh
"Ooh" is most certainly a word. As is both "Ah" and "Aah" https://www.oed.com/dictionary/ah_int?tab=factsheet#8068455