Echo effect when viewing movies/tv

Question

What can cause this? I have Comcast DVR with HDMI to TV; DVD/recorder with HDMI to TV; optical from DVD to receiver; optical from Comcast DVR to receiver.

I am considering re-configuring it this way: HDMI from Comcast DVR to receiver; HDMI from DVD/Recorder to receiver; and HDMI out from receiver to TV. Would that make a difference? Do I still need optical and, if so, where? Thanks.