Oil leak and whistling sound

Hey Guys,
I have a 2006 Tacoma 4 cyl 2.7 with 45,000 miles and I noticed the other day when I started it up before work and let it idle a bit I smelled burning oil and I could hear a whistling sound. So I looked under the car and noticed it was wet with oil right below where the altenator is on the engine but can't tell where it is coming from. The whistling sound is coming from that same area. Any ideas what this could be?

 

Check the valve cover gasket. Wipe a towel around the edge to see if you can locate it. Also check if the vacuum hoses are connected right and that your air filter isn't clogged.

 

Valve cover looks clean and I cleaned my K&N filter a couple months ago. I also noticed its wet with oil around where the belt tensoner is under the alt.

 

I just checked the valve cover again and it seems to be leaking just a bit in the back so I guess its not to bad. But what is causing the whistle sound?