I've always had a fascination with the consonant sounds p (in a lesser degree, b as well) and k (and hard g like in "goat"). So when I'm reading something, I tend to pronounce all the words with those sounds under my breath so no one can really hear me. And then usually the last word with one or both of those sounds gets repeated for a while, but never so that other people can hear me.

I also type into the air, something I started when I learned business keyboarding in 6th grade, and it's usually the last phrase or sentence someone said to me. Sometimes it's while they're still saying it. I also type out the lyrics to songs in the middle of worship. Can that be considered echolalia too?