I run PR1.2 since the day it arrived. I've never had real responsiveness issues. Nor do I really push the screen as I would push a keyboard.

However, a gentle touch which goes just a tad bit more than what you describe (hardly touching anything on the screen at all) is enough to create the sound, just as afaq mentioned. The click isn't there every time. However, the whole top part of the phone makes these clicks and rattles every now and then, and I am wondering if the frame would have got loose. Given that the phone has never dropped even on a carpet, this is a bit surprising.

I will probably take it to Nokia as you suggest. Since there's a guarantee, I am not going to try to open anything myself.