Weird Engine problems

So I have a question!! My car has been acting very funny lately.

1. I had a valve seal leak(fixed) and my timing belt is leaking still.

2. My mechanic says the baffle inside the Intake manifold has broken loose(anybody explain that too me please!!)

3. A loud metal on metal vibration noise. someone at school said it could be a loose heat shield on my exhaust(please help)

4. Now there is a noise like a lot of pressure is being released and I don't know where from.

5. Also I had an OBO error code P0171(lean in bank 1) earlier last week its gone now but I don't know why I got that error.

Somebody please I could use some help here!!!