I am hoping to hear from you experienced YZ-450 owners on something I noticed about my ride during breakin yesterday. I bought a left over 04 Yz-450 in January and have been staring at the thing for months in my shed. Well, I finally got to ride the thing yesterday to break it in, and noticed a whistle that I couldn't locate. It got louder the more I gave it throttle. I called the dealer and they weren't a lot of help other than to check the head gasket and other obvious areas for leakage. They did say to bring it in and they would check it out though. I took it to the dealer today since I could not find the source of the whistle, and lo and behold, the noise is the sound of the air going through the boot/filter. They spent quite a while trying to figure it out, until they took the seat off and it got louder. We tried putting grease around the filter bolt hole, and this didn't help. All they said was to try another filter. At least it doesn't;t sound like anything mechanical. I am worried that there may be a leak somewhere that we didn't find, so is there anything else I should look for, and has anyone else had this happen to them?