I recently purchased my pair of DT770 Pro 250 2nd hand and like many, they had the 'Death Rattle' in the left ear (it seems common for always and ONLY the left to be affected). Like yourself Lawrecednt, I opened up the cups and cleaned out the crap that had accumulated inside; it seriously looked like what one might find under their couch cushion or car's floor matts. Like you, I had limited success, with the rattle coming back a few days later. And like yourself, I thought could it be the cable or maybe the cover rattling? So I grabbed some foam and wedged it beside the cable and I also put some foam pads on the cover stops on the inside of the cup to anchor them better. Again, limited success, as the rattle came back. Oddly enough, no matter how I rotated or positioned the cups, the left would rattle BUT when I reversed left and right on my head, the rattle was gone. I simply could not get the left driver to rattle when on my right ear. Bizarre!
Anyway, I am just going to throw this out there, but the rattle WILL come back. The problem is 100% hair on the driver's diaphragm, and by that I mean the thin film, not the white fuzzy cloth on the grille. I wish I had taken pictures, but the left driver in my DT770 Pro looked like a poodle.
Here is my 'fun' experience:
So after about a week of trial and error (read above) I finally took the plunge and completely disassembled the left driver assembly. This was surprisingly easy to do. All I needed to pry off the snap ring and driver/magnet covers was a small flat head screw driver. Everything else I used my fingers. Kudos to Beyerdynamic for making these cans user friendly.
At first glance the diaphragm looked nice and clean. I then took an LED flashlight and shone it at an angle over the film. Wow, I never expected what I found; At least a dozen hairs literally stuck to the outside of the diaphragm's film! All the hairs were curved around the diaphragm, but fortunate for me they all had at least one tip pointed outwards. So I took a plastic toothpick and a pair or tweezers and proceeded to lift and pull off the hairs all in one breath; my nimble hands were rock steady. A few hairs actually came off in clusters which made the task somewhat easier.
Only one hair remained, and this hair was directly on the dome. Not just on but coiled around with no tip visible. Lovely eh? I almost overlooked this one...almost. I carefully found a little wiggle room and was able to lift up a portion of the hair, enough to fit one blade of the tweezers under. YOINK! <---the sound the magnet made as it grabbed the tweezers, collapsing the dome. Sigh....Lucky for me, as stated, my hands were rock steady, and so the magnetic pull was gentle (but VERY strong) and the film was intact. Ok, no problem. This just meant I had to actually pry out the magnet to avoid any further grabs, something I should have done in the first place. So out comes the magnet and I was able to successfully pull off Coily which when stretched out, was an inch long! I then used the round handle tip of a screwdriver and pushed out the dome. Besides a slight cloudy line on the dome, all was 100% perfect.
The most difficult part of the whole process was hammering the magnet back into the driver assembly. Needless to say, it is an extremely tight fit. I could get 2/3 of the magnet in by hand, and for the edge that was still sticking up I placed the driver diaphragm side down over the edge of my desk (so that only the frame touched avoiding any film contact) and used the handle end of a screwdriver to hammer it back in. FYI, the magnet is very strong. Like insanely strong! It could probably hold leather to a fridge strong!
Anyway, I hope that my tale can be of help when you think all else has failed. It just takes a little bit of time and patience, but well worth it in the end. Who doesn't want great sounding headphones?
