I just recently got my fuel filter replaced and the fuel pump whine went away.. and the car is running much better.. But there is still the hissing come from right around the fuel filter.. My mechanic claims its normal, but its definitely louder than it should be.. Could it be one of the hoses is loose or has a slight leak and where should I look exactly?

 

I would assume if you had a loose connection and the hissing was coming from that then there would be fuel spraying. The only connections are fuel lines so it's not like it would be just air coming out. I don't know what else is in that area that would cause that, but can you smell fuel?