I had the same problem and went to a local exhaust repair shop and for 20 bucks they replaced the hanger. It's a beautifully welded onto the pipe and then bolted onto the body with rubber grommets and everything. Actually I had them do three different hangers, and now my exhaust is excellent ; and I'm out 60 bucks....totally worth it!
Is it the exhaust hangers or the mounts? The hangers on the OEM exhaust are very burly. The rubber mounts on the other hand do tend to succumb to age and...rocks. Replacement non-oem mounts can be had fairly cheap. I'd check and if those are shot, just replace the mounts. a few bucks for some sanity till you replace the whole exhaust. I *think* this is the part I used: http://www.amazon.com/dp/B00180J90I/?tag=ihco-20
Have new nuts on hand before you start. The old ones will not be reusable. The bracket which sits below the rubber mount is itself removable, so you don't have to move or remove the exhaust to replace the cushion/hanger. You'll need just a ten and twelve mm socket/wrench. Ten minutes and you're done.
I rechecked the location of the noise with the truck tires chocked, in drive, with safety person in truck with foot on brake. When the truck is rev'd slightly it sounds like the rattle is actually from the muffler and not the clamps/supports/hangers. I think this is the original muffler/exhaust system with 290,000 miles so its overdue to replace anyway....
I took the truck in to local muffler shop. Noise is coming from the actual muffler. The shop cant get replacement, but will install OEM muffler if i bring to them for 100 bucks. OEM muffler is $471. All other pipes/brackets/hangers appear good.