New Year's Shinto Altar Decorations

Everyone, do you decorate your home's Shinto altar for New Year's? You might find having a Shinto altar itself unusual, but my grandmother has one, so she'd prepare decorations every year as New Year's approached and place lit candles around that time. However, out of the two candles placed for New Year's, only one would consistently flicker. I was always bothered by it, and one year I mentioned to my family, 'The candle flame is flickering during New Year's.' My grandmother said, 'Perhaps a deity has visited,' but my mother, being easily scared, insisted, 'It's just the wind.' But my grandmother's house is in Hokkaido, and New Year's is in the dead of winter, so the windows aren't open. If it were the heater, I feel like the decorations around the altar would also sway, and more importantly, I don't understand why only one flame flickered. Later, when another New Year arrived, my easily scared mother pointed to the candles, remembering what I'd said, 'See, they aren't flickering now.' And indeed, they weren't at that moment. I kept the fact that the flame had flickered a little later a secret. Have any of you ever seen a Shinto altar or flames behaving strangely like this?