Is it normal to make vague sounds rather than speaking with words?

For as long as I can remember I've often made sounds instead of replying with words to people I'm speaking to. When I'm embarrassed or unsure of what to say, I pretty much always make vague noises in the back of my throat which could mean anything. Some words, however, I've almost completely replaced with specific sounds. Goodbye, for example, sounds something like 'Ynunnh', and I make a sound something like 'myow' when someone asks my opinion of something and I want to say that I think it's so-so. The same sound, but higher pitched, expresses interest. As a child I used to hiss like a cat when anything upset me, and I still do when I'm startled.

Obviously I know exactly what every sound means, but I think people who don't know me well think that I'm just making random noises. Does anybody else do this?