I doubt it would be the clock spring, but there are a couple of wires coming out of the clock spring that might be rattling around behind your airbag somehow. If you want to try to fix it yourself, you can start by taking off the plastic panels around the steering column. Two philips head screws on the top panel, 3 on the bottom panel. Maybe try driving around with those off to see if the clunking goes away. I'd go along with the previous suggestion that it may be the rubber flap between the dash and the steering column. Mine was a constant noisemaker. Complained about it to the dealer and they basically broke it in trying to fix it. Eventually it broke all the way off, and I don't miss it.
If you take off the steering column panels and can't figure out the noise, it might be one of the aforementioned wires stemming from the clock spring. However, if you don't trust your skills you might not want to take this one on. You'll need a 20mm hexnut drive to disconnect the airbag screws, and you'd need to disconnect the negative terminal on the battery for at least 20 minutes prior to doing any of this. Otherwise the airbag could go off by accident (it holds a reserve charge for a little while, hence the need to wait the 20 minutes). The clockspring is like a ribbon cable that controls the airbag, cruise control, and horn. It's easy to damage, so make sure you don't bite off more than you can chew, and good luck on finding a fix.
Jim
