Originally Posted by SSJup81
It probably depends on the person listening. I know that some English teachers I've had was very strict where grammar was concerned, and would get on students vehemently if mumbling when talking or using "um" or "hmm" and such, like we were hesitating in our speech.My Japanese teacher does this. I've noticed it.Ironic, my teacher has done this before as well. I found it odd, then figured that since she was on a cell phone, she probably thought she might've had a dropped call.
This is called aizuchi. It means doing what you described to show the speaker that you are listening. It's considered polite and necessary.