Low moan from hood at high speeds

Hey guys I drive a 2002 Acura Tl type S 3.2L and have a low moan that sounds like it's coming from the hood when driving at high speeds. Basically the faster I go the louder it gets.

My rpms don't shoot up or anything like that. The transmission was replaced about 80,000 miles ago.

I was told it could be the spark plugs but after replacing them the sound continues.

Any help would be great!
Thanks!