Just recently, i have been hearing a noise coming from the interior vents of my 2001 es300. Its as if there is a constant cricket noise and it only happens when the fan is on. Sometimes it will occur all day, go away for a while, then i hit a bump and it came back. It doesnt sound like the alternator belt which someone told me it could be, the sound is only coming from the vents, not the engine compartment. Does anyone know what it could be?