On my way home I got in my car to leave work and started it up and it started making weird noise like the fan was riding on the shroud or something. I check the fan clearance and it's fine. So I went to the store to check my oil and it was low. After I added the oil everything seemed fine until the RPM reaches about 3 grand and it starts kinda knocking or something. When I got home I started to rev the motor a little and I can hear something making noise in the valve cover can anyone help????