I haven't been able to find a good answer, but I'm wondering if it's something that I do. I've always liked using silly voices and accents, and I've noticed that I often use them as a way to dissipate tension when I feel nervous or awkward about saying things, like when I need to ask someone for something or when I need to assert myself and I'm afraid it will sound angry or mean. It's something I'll only do with people I know well, though. When I encounter such situations in public, I just become very awkward and tongue-tied, with lots of ums and uhs.