Variation of channel attenuation with frequency
No, there would be no local attenuation over the 10MHz subcarriers at 1800 MHz of any significance if you exclude the multipath effects. The standard path loss equation holds and this would be a non-dispersive (linear phase) channel with minimal difference in attenuation across the 10 MHz band. However, due to multipath fading you can see significant changes depending on the delay spread of the signal due to the fading environment (frequency selective fading). 

See the figures below to get a sense of the delay spreads at 1.8 GHz for different environments and its effects on fading.





In the simple model of a direct path and a delayed path both of equal amplitude, you would have frequency nulls spaced at $f= 1/T$ where T is the delay in seconds and f is the frequency spacing in Hz. This gives you a sense if the delay spread involved will result in flat or frequency selective fading. For the three typical delay spreads listed relevant to your 10 MHz channel, the spacing is 5 MHz (for 0.2 us open areas), 2 MHz (for 0.5 us suburban) and 333.3 KHz (for 3 us urban). Of course the nulls won't be so evenly spaced as in the figure as multiple delay paths are involved, but this helps give a first order metric as to the frequency selectivity of the fading.