I have about 10 domains and it is really strange that all the sites does a google dance all the time at the same time. every few weeks all the sites starts getting traffic for some days. then the google dance starts again and the traffic minimize to -90%. after few weeks the sites are coming back stronger than before. why do all the sites loosing traffic the same time? should i delete my sites from google webmaster tools? p.s. most of them are 1+ old.