loud noise comeing from air intake

i have a 2002 f150 supercrew 4x4 i have 70,000 miles on it its been maintained well i have a loud noise comeing from the top of the engine sounds like its comeing out the air intake it does when i idle or rev the motor or even going down the road any help you can give would be great (its a triton 4.6 v8) its like a sloppy exhuast sound from under the hood could it be timeing or a plug

kevin