The tone of his voice got changing and changing, becoming harsh, and with that it attracted unwanted attention.
Gradually a quiet exasperation crept into his voice, enough to attract attention (and perhaps other feelings - abhorrence, apprehension, inquietude, worry, etc.).
I could say that "while people around us stared with a questioning looks.", but the very fact of attracting attention convey that.
And somehow, one could think one of the parties from ones in the harsh conversation/discussion would have to look around (albeit a sideway look, to feel that.)