It's not clear to me if either
Pannam or
A16X100 have new or second-hand headsets, however the issues do appear a little different to me.
I wouldn't classify 'static/crackling' as a 'buzz' but I'd suggest the former could simply be a result of a bad connection somewhere whereas the latter may be an issue with the electronics - albeit low voltage might also cause something like this.
FWIW I claim no particular experience with DC headsets and cannot comment on whether these are common issues with this model, but I would be inclined to thoroughly check any battery connections, and that the battery voltage is up to spec. Given the way NC typically works I'd also check that no ancillary mic passageways are blocked - note this is not necessarily the primary speech mic.
Obviously if these are new units they should be returned for warranty repair, however I'd like to think it possible to check these few things first without doing anything intrusive that would affect a warranty, particularly if it's difficult to access a repair centre wherever you are. Should you come across anything simple that fixes the problem it might be useful to others if you posted back on that.
FP.