This is one of those words that has barely entered into the written language. It is sometimes written as two words, "hirdum dirdum", or hyphenated, but usually it just isn't written at all. (These days it isn't even spoken much).
"My troth, I wuss we havena to sup lanten-kail and pree barefut-broth after siccan a hirdumdirdum!"
-- Tylney Hall, by Thomas Hood 1840.
Hirdumdirdum is a noun meaning an uproar, a tumultuous noise, a mess, or general chaos. It may well have other meanings in various contexts, but as it is not listed in any dictionary that I have found, I can only define it by my own experience.
It is found in Scottish dialects, and may occasionally make appearances in other UK dialects. It seems to be an elaboration on the Middle English durdan, meaning an uproar or a din. Durdan entered the Scottish language in the form of 'dirdum', which is still used today to mean 'blame'. I have been unable to find the source of 'hirdum', which may have just have been added on because of the pleasant consonance.