There is a "ringing sound" inside the cabin, it seems to be coming from the back seat area, when I drive the truck at higher speed on the highway. It is somewhat intermittent although it was constant the other day. The road surface is a bit rough as the highway is somewhat grated. My tires are old, good tread still but they are the originals and have surface dry rot (will replace them next week). Had rear brake pads replaced. Still the noise. The road is like if you would have loose nails in a glass jar that were vibrating. I'll check for loose parts everywhere and can't find a thing. This started a few months ago. Any ideas?
Noises are something we can't help diagnose even more so being intermittent. It can be anything from something being loose or even something not being secured at rear. Tire vibrations etc can elp to amplifiy such noises.
Get someone to sit ate rear and note where the noise is coming from and zoom in at the source area.