Unknown sound???

The past few days my Jeep has been making a "whining sound" when I start her up. It usually goes away after a few moments, and doesn't come back again until I go to start it up. Except tonite, when I went out to get it, the sound never went away. It's a "whine", and I'm hearing it from the pass. floorboard. That's at least where I think it to be coming from. I'm kind of leaning towards the transmission to be the source, but I'm not for sure. Tonite, it made the whining or whistling sound when I would go to slow down, and sometimes when I gave it gas. I also noticed some oil leaking near a leak of coolant. It's near where the heater core is, but it's not coming from there, I know. So, what do you all think it could be? Thanks for any help.