Have you tried different cables?
How do you have the 5005 connected? Which inputs are in use, etc?
Try connecting the 5005 directly to the TV using the RCA connectors, but only connect one of the audio channels at a time. See if the hum is present in both channels or only in one of the two channels. Do not connect anything to the inputs on the 5005. Just connect the outputs to the TV and play a commercially recorded DVD.
If this checks out OK, then connect the Tivo to the input side of the 5005 and see if the hum returns. If the hum is presnt without the Tivo then the input side of the 5005 has nothing to do with the problem.
Post back with some results and lets see if we can narrow the problem down.