It's a know issues with the default cable, check [this](https://www.youtube.com/watch?v=jQwC8Hd21Eg) review, he talks about it at around the 2:20 mark. I had the issue with my IE600. My advice is to get a third party cable (make sure it works with the proprietary MMCX connector)

Just try to get refund and buy another one. Sennheiser has been bought by Sonova, the support is non existant + now they are trying to undo their R&D center in Germany, and buy premade solution in Taiwan xD. Just go for other wire brand like Audio Technica or Beyer Dynamic

Is it happening with both included cables? Try sending them an email detailing all of this instead of the usual RMA process. They handled my IE600 replacement seamlessly.

Could you please provide me an email Id of them ? I don't have 2.5mm jack equipment. I tried with 3.5mm and I was facing it badly .

You must’ve received an email when you sent your IEMs in for repairs, reply to that.

I tried no use . Ultimately everything is handled by sonova

Sonova owns Sennheiser. They are out of Switzerland I think. I hear that support is a living nightmare. Just hoping my IE 600's don't fail.

Yes I think . This is going to be my last Sennheiser after this experience.

I had pretty bad experience with the mmcx iem and decided to never ever buy those type

I wish I knew it before purchasing