Pronouncing '-old' as '-oul' or '-ould' (or if you like '-owl' and '-owled') is common in many parts of Ireland and in fact also some areas of the UK such as Liverpool which have a long tradition of Irish immigration. It's akin to what the Scots do with '-auld', as in 'Auld Lang Syne'.

For example the term "bleedin' oul wans", from "bleedin' old ones" was once very common in Dublin to describe older women who the speaker regarded as interfering and old-fashioned. Some people still refer to their father, mother and parents as "the ould fella", "the ould doll" and "the ould pair".

Personally I still say things like "she's could (cowled) enough today" on a cold day, which anyone from where I grew up in Donegal would recognise.

I suspect this comes from Old English originally, for example this discussion of the poet Milton indicates that this pronunciation was common in his time, and possibly came to Ireland with the English and Scots.