As you stated, I get this when I run in the cold. One explaination is that cold air thickens your saliva, so you begin tasting a blood/iron taste. It would be safe to say that similarly if you become dehydrated and lose saliva you would have a similar taste. Try to stay hydrated, if you get this feeling, get some water and salt back into your body. Also quit smoking, I'm sure that increases the badness of everything bad.