Rolling Rs

Here's a thing which makes me wonder why, and makes my girls laugh:

My "r" rolls sometimes. (Yes, sometimes, not all the time.)

It suddenly started some months ago. I would say it was... at the end of last summer. A big surprise because I hadn't been able to do such a thing however hard I had tried before. Remember myself, a student who was hugely into phonetic, practicing in vain on the way home from uni, which was more than 10 years ago. (Always made sure there was nobody near me.) Well, I first noticed my rolling "r" when repeatedly telling my girls, "Brush your teeth! Brush!" just before their bed time.

At first, it was only when "r" was just after a consonant at the start of a word. Eg) "prat", "brat", "try", etc. Now it happens even between vowels and at the start of a word. Eg) "hurry", "right", etc. But unfortunately I can't control it. If anybody tells me to roll "r", I can't... It just happens sometimes. Strange.

I'm 99% sure this is nothing to do with listening to Rammstein too much as my "r" started rolling well before I got hooked on them. I don't speak or listen to languages such as Spanish or Russian. However hard I try to find out why/how it started, I can't find any answer. Maybe there isn't any answer for this. Why does "r" roll in my mouth? Oh, I don't know. Maybe I don't need to know...