I also find listening to my own voice painful. Lots of people do, I know, but for me it's the monotonous quality you mentioned, which many aspies have. I speak in a flat, west coast American accent, which is pretty generic as far as American speech patterns go. I also get asked to speak up a lot, although I don't think it's my actual volume so much as the pitch of my voice and the lack of inflection.
When I was younger, I worked in retail (a nightmare in and of itself) and would sometimes make announcements over the PA. I was asked to do them because I supposedly had a calm, soothing voice (flat and boring?). Whenever I did the store closing announcements, I would get teased afterward that I sounded like the announcer at an airport. People would see me and spontaneously say things like, "flight 732 non-stop to Seattle is now boarding at gate 32c." Then they'd reassure me that my voice was very pleasant. I think the fact that they felt the need to reassure me immediately after poking fun at the way I speak drove me nuts as much as having to make the PA announcements in the first place.
Now I work in the HR field, mostly with payroll, benefits and legal compliance issues. Once in awhile, though, I have to talk to a group of newly hired employees and I always obsess over how I sound in front of the group...like a boring college lecturer, or someone more engaging that makes them feel like a welcome part of the company? Probably the former, but I'm learning to live with it. Just don't make me listen to a recording of myself!
