Scared the **** out of me..car revs sounds like siren, wut do lol

woke up and started up my car, everything went smoothly went on the freeway then got off 30 minutes later and literally when i accelerate i get a faint "police siren" sound..i **** myself when i heard it because i thought a Popo was chasing me (typical BMW drivers on the freeway)



car somewhat sounds like this

http://ift.tt/1OOqWvY



what can it be? i changed all my cooling system and pulleys...can it be a leak in my air intake?