[cjc]

 I've owned the HE-400's for over a year with no issues, and just noticed the left earcup has a rattle noise.
The noise sounds like a tiny loose nut inside.and nuts were accounted for.
Where else might this rattle be coming from?

 

[cjc]

I forgot to mention, the rattling noise is NOT audible...I don't hear it while listening to music. 

 

[sarahthefox]

I just bought a new pair of HE-400's that also have a rattle in the earcup. I don't hear it when I listen but it can be heard when they are shaken or moved on my head. Wonder what it could be...?

 

[cjc]

Sent my pair back to Hifiman and they quickly repaired/replaced and No more rattling, Glad they were still under warranty.
 Glad my Audeze LCD-2's have a 5 year replacement policy.

 

[Soundpitchblack]

Hey I know this post is quite old, but I have been noticing the same on my new HE400S. Did you email them or called them? which method is the fastest ?  Thank you for the help.