The HDHR is very chatty, and it's all UDP streams, which can affect the switch buffers on inexpensive Ethernet switches. As Thom said, if you have a layer 2 switch, putting it on it's own VLAN, or applying QoS are two possible options. I just put my HDHR on a dedicated non-routeable network adapter and switch, and configured MythTV to look for it on that segment. It eliminated a lot of weird network issues (and I did that long before buying a Layer 2 switch).
HTH!
/Mike