1) the noise ‘prumpth’ is used in situations where the speaker is unable to think of a suitable answer to a question.
2) it can also be used as a gesture suggesting a lack of caring or a certain indifference to a situation or object.
-oi have u seen my phone?
-purumpth(this is often accompanied by a casual shrugging of the shoulders)
-did u eat the last of the good cheese?