I just went over 100k on my Tundra. I have had zero problems with the truck until recently. When I accelerate there is a strong howl that comes from the engine compartment (it like like the typicial intake sucking sound but ...the pitch is pretty high.) I changed the oil (royal purple is what I run) and changed the tranny fluid and filter (Toyota WS fluid with OEM filter). There was no change. I checked the fan cluth and it is fine. I also ran techron through the engine fuel system twice. I took it into my local dealership and that said it is my K&N filter. I am pretty sure it is not because it makes the same noise with the filter out. I have check everything and everything seems tight and the truck is actaully getting 18 mpg on the highway which is as good as it has every gotten. It has the sound regardless of the outside temp and regardless if the vehicle is warmed up. It does not make the noise when it is at normal idle...so I am at a loss as to what it is. Any suggestions of what to check would be much appreciated. Thank you in advance for any suggestions.