Thanks to everyone who offered me advice on how to handle the artifacts. I have a new question - I'm looking for ideas for strange or mysterious events or sights that might happen to the PCs. The catch is that if these events have any trail that the PCs can follow, they WILL follow it, thus derailing the plot and frustrating them when it doesn't go anywhere (in their defense, they are usually trying to be loyal to the plot and assume that anything odd that happens is a plot hook). So, these events need to be things that the PCs have to make note of but can't act on, something to keep them puzzled and off-center. Please offer some ideas? Here are some examples, from www.roleplayingtips.com
A phantasmal image just on the edge of the vision of 1 character
A voice in 1 character's head (IMing messages to that player, so that it's more mysterious)
A feeling of deja vu in one or more characters
A ray of light seems to surround 1 person
It's eerily quiet
When I say that my players will take any trail and follow it, I really do mean that. If a beggar tries to sell them a ring from the sewers, they will interrogate the beggar, buy the ring and then intensely analyze it for any magical or historical clues. If an ox died in the street and caused a block in traffic, they would probably assume it is the work of Chemosh (god of death) and insist on doing a autopsy on the ox to find out why it died. Then they'd get frustrated when I told them that it died of natural causes.