That metal channel is called vally flashing. Sounds like you could have an ice damning problem in the winter. This is mainly do to insuffiecient ventillation and insulation. Of course contributing factors are if your bathroom exhaust fan exhaust into the attic instead of out through the roof. Along with lots of other penetrations that could be allowing warm air up into the attic space from below. Here's a link that'll tell you about the causes and cures for ice damns, hopefully it'll help you out some.
http://housing.cce.cornell.edu/f-sht...ndensation.pdf
You can also buy some heat cables to stick up there in the winter time that will help to prevent the ice from ever occurring and allow the water to flow down into your gutters and away. Let us know if you need more help or info.