[paulat (OP)]

When a train on which I was travelling recently (yes, it was moving, and on time, and I could afford a ticket (that's what's called a miracle!)) entered a tunnel my ears "popped" like they do on aeroplanes. Why does this happen?

[Karen W.]

I would think the air pressure change in the tunnel effects the pressure inside your ear, but I am no expert and can't tell you why..perhaps at a guess it causes more pressure inside or something and your ears might pop to release the pressure buildup.. who knows I am just hazarding a guess..