Did you get yours replaced?
I just got a refurb replacement that has this exact problem. I've attached some photos.
I'm getting really sick of these dodgy refurbs.
1st iPhone 3G - Hairline cracks
2nd - No 3G, poor Wifi reception
3rd - Hairline cracks, couldn't connect to wifi networks
4th (current) - Light leaking from the whole left edge, lens problem