we've been videoing an artist recently for some friends with two videocameras one of which was getting the sound through 2 radio mics (Shure) fed into a mixer (DV promix 3). We've tested them before and they seemed to work fine. When we checked the footage though we almost got a fit: there is a constant hiss in the background, which couldn't be eliminated. Not remembering if we powered the mixer through the mains or batteries (we suspected that connecting it through the mains might have caused the problem), we've repeated the test but it seems to be working fine - ie no hiss with or without power from the mains.
Luckily the microphone of the other camera was adequate enough to make the final product presentable (they weren't after an amazing quality) but we really need to make sure it won't happen again... Here's a link where you can hear a small section of it:
We thought it might even been caused by interferences with the radio mics?
Any suggestion would be appreciated!
I'm going to guess that this is an RF problem or a problem in thedifference between input and output levels of the transmitter and receiver, raising your noise floor, based on the hiss. Power problems usually mean a buzz, not a hiss. This is only a guess, withotu seeing the gear first hand.