I didn’t use my Sennheiser MM 500 for long time but resurrected them a few days ago to compare these to my headset provided by my employer. I realized a weird cracking in the left ear which reminded me why I didn’t use these pairs for a long time. I decided to figure out what exactly causes the sound issue. After taking away the ear foam there is a mesh which also have to be dismantled. I checked the speakers and realized two plastic parts. After a little bit search I identified the small high tone speaker on top of the main speaker. The seat wall where it is pressed in is broken – on both sides. The mic still sits great there. After gently pulling out the broken plastic parts the headset is working like on day one… Give it a try if you own a pair of these, it is worth it.
The exact same thing happened to my pair. It was especially noticable on the bus, the vibrations caused by the engine made these little plastic pieces vibrate against the speaker membrane. I initially thought the battery pack was wobbling around in its slot.
After I removed the little plastic pieces I used some hot glue to keep the high tone speaker in place. And there you go, problem solved, no more cracking noises!
Thanks for sharing this!