One of the most undervalued roles in Toastmasters is the "Ah-Counter". This person's function is simply to note the number of times speakers use "ah" or "um" in their speeches throughout the evening. Of course, "ah" is a nervous tic and becomes annoying when repeated - often unconciously - several times in a row. But the real issue - once again - is status.
Your voice is an essential tool in communicating in language - as obvious as that sounds, it's equally stunning that so many people neglect it. Voices can be high-pitched and nasal, creating an unpleasant effect; other presenters rarely breathe during speeches, creating a machine-gun effect; others snort, suck in air, or speak too quietly - all variations on the "ah" in speech, for they all exhibit poor personal command, and thus low status.
Record yourself. Yes, it hurts - but how do you think we feel? Take a text ("elicitation texts" are available online for free: they are created to sample all vowel sounds and consonant clusters to test for regional dialect variation). Keep reading it and recording yourself until you are happy with the way you sound. Remember that the recording hardware will affect your voice - on my cell phone I sound tinny, with better equipment more sonorous.
Professional actors have a stage voice - there is no reason why you shouldn't have a - pleasant, commanding, and intriguing - professional voice.