Removing noise without destroying details is a difficult challenge in any digital manipulation, as blurring tends to eliminate both.
The Reduce Noise feature found in the Filter>Noise menu has limited effectiveness on really stubborn artefacts, but if nothing else seems to work, give this trick a try.
Switch to the Channels palette and click on each one individually. A close inspection of each channel will reveal that a majority of the noise is present in one channel more so than the others.
Try the standard blurring and noise removal techniques on just that channel, as that way the details held by other channels are left intact.