Hi,
its possible, that the noises are from a harness, who goes direction to the trunk. There often not good fixed in the stang. You have to remove the side interior to see the wires. Fix everything and protect the interior contacting parts with foam tape. The noise is probably from the rear interior part. Try with your hands and knock on the parts. The best is, if you have someone who can sit in the rear while driving and try to locate it more exactly.
The last 2 years i fixed around 10 or more noisy points in my stang. Now he is quiete.
Good luck!
Greetings from cold germany

Mario

 

I have the same annoying buzz/rattling in my e-brake handle. If you figure out a way to fix it please post it. Drives me nuts and I end up driving around with my hand on the handle to keep it quiet.

 

I took my mirror apart and it's tabs inside that are broken that rattle so I super glued it back together and no rattles now

 

I looked at it today and thanks to your idea my awesome girlfriend volunteered to hang out in the trunk while I drove around. She was able to pin-point where the noise was coming from. When we got back home I tore into the trunk looking for a lose harness or maybe some lose metal. Didn't find anything. Raised the car up and removed the drivers side rear tire and started looking around the area she indicated the noise was coming from which was right where the muffler was hanging. I started to shake and move it around and BAM, there it was. It looks like the muffle wasn't tightened correctly and had jarred lose. It's hard to explain but the metal are from the rear of the muffler was moving in the rubber grommet causing that noise. Put the exhaust back in place and tightened up the bolt then went for another drive and the only thing I heard was the sweet sound my car makes when running.
Thanks!!

 

I had that problem once with a previous Mustang I had. The rattle started after putting on flow masters and it only happened during a certain RPM. Does the noise stop when you put your thumb on the e brake button? What I did was find some foam packaging material, while holding the the button in I crammed as much of the foam material inside the handle as I could get, which wasn't much but it was enough to keep what ever was moving and rattling from doing it again.

 

I looked at trying to do that tonight but even with the button pushed in I don't see how I could stuff anything in there. It will stop if I just put my hand on the handle.

 

Found a nice solution to the overdrive button rattle in my automatic shifter. Took some shrink tubing and wrapped it around the circumference of the button. Shove one end of the tubing in there, then just snake the rest (just a few inches) around the button a couple times. Use black to keep it inconspicuous.