After hearing this on ours, I did some searching I found a couple of reports on this, but I was wondering if someone could confirm it.
It seems that on channel 2 (internal) there is faint high pitch sound every 1/2 second or so. You would probably need to be listening to room tone to catch right away, but once you know it's there, it becomes an obsession of course. This was from an MKE 2 plugged directly in input 2 and feeding both channels.
I should add that this was on a sound stage, I could hear it in my cans during recording, but it wasn't in the room.
Send an email to pbtscservice.com and describe your problem. They will email back with the service location for you to send it to. There is a fix for this and it is not related to the card at all. It is a warranty repair.
Jan Crittenden Livingston
Product Manager, HPX500, HVX200, DVX100
Panasonic Broadcast & TV Systems