I recently bought a 2001 Silverado 6.0 liter 2500 with 130k miles. I noticed that i hear a rattle when it reaches 1500 rpms. It never rattles at any other rpms. I already removed the manifold covers because they were rusted but i still hear it. I checked the exhaust from front to back and can not find anything that will rattle but yet it continues to rattle at 1500 rpm. Any body have an idea to what this could be?