In the first season at episode 8, before Grand-Fisher leaves for the world of the living one of the rocks casts a large shadows before 4 other shadows shoot out and take form on rocks around Grand-Fisher, they apparently speak to him as he replies that he'll go and deal with Ichigo himself
I am wondering who these shadows are and if they are related to Aizen or are they a separate faction that don't support Aizen
EDIT: got some screenshots, there are 4 shadows but we only ever see 2 close up