I think my truck has an exhaust leak. There is a buzzing type noise that increases with RPM. I can't hear it with the windows up, but with the windows down on a quiet street or while driving by a wall I can hear the buzzing. The noise is louder/more pronounced when the engine is under load (accelerating in gear) than when I rev it in park. I have replaced the manifold to downpipe gaskets and both catalytic converter gaskets. I have yet to replace the O2s and associated gaskets, or the muffler to resonator gasket. The noise seems to be coming from the front half of the truck though, so I don't suspect that last one. Heat shields are tight, bellhousing-to-downpipe clamp is snug, no broken exhaust mounts that I can find, and no visible contact points on the frame or sliders. My first suspicion is an exhaust leak, but I am having a hard time determining if there are any leaks. What methods do you use to find exhaust leaks? Feathers, flames, high priced sniffers? The second option is that it is not an exhaust leak. At this point I'm running out of other ideas for the source of this sound. I read Doug's post a week ago about the aircleaner tube rattling against the fender, but I've played around with that to no avail. Other ideas would be welcome at this point.