I have developed a constant pitch whistle (about the high E string on a guitar) in my '96 FZJ80, but only when the throttle is applied. The volume increases with the throttle, but the pitch stays pretty much the same. It started a few weeks ago and has become progressively louder. The sound appears to be coming from the rear half of the engine compartment, but is not present when the engine is cold. I also cannot generate the sound either by reving the engine without load nor by reving the engine while in gear with the brake applied - I must be moving at least 10-15 mph. A vacuum leak came to mind, but I would think that would be worse at idle (when manifold vacuum is the highest) and this gets worse with throttle. Maybe I am missing something here? I have had an intermittent P0401 which I will be trouble shooting this afternoon, but I've had that for some time and the whistle is only a few weeks old, so I am assuming they are not related. I checked the tranny level yesterday and found it it be 1/2 qt low, so I suspected the torque converter may be the source. However, the noise persists after bringing the tranny up to the fill mark. I've struck out searching the Mud archives, but it could be I am not using the correct keywords (whistle, throttle). In any case, I am at a dead end and am looking for ideas. Thanks!