Don’t judge too quickly. Read more at http://www.independent.co.uk/life-style/um-like-filler-words-discourse-markers-why-use-er-you-know-a7665721.html. Excerpt:
Long considered to be a sign of stupidity or ineptness, linguists are saying this is unfair. Often, the people who make these sounds, in between actual words recognised in the English dictionary, are being especially conscious of who they are talking to.