I've an inexpensive pair of Sennheiser earbud type phones that I have previously a-b'd against my 2 other pairs and found largely similar, ie no noticeably nasty artefacts.
I just converted (wav-mp3) a tune we recorded and checked it on my buds and it sounded terrible, overly bass heavy and a little distorted. Went to get my good headphones (over ears)to rule out pc soundcard or conversion issues and, thankfully, all sounded fine.
Is it that the buds have somehow deteriorated (but both channels the same?) or the fact these go in my earoles not on them?
If I had to guess from the sound, it's like they've got fluff in them pressing on he diaphragm, but they look clean enough and the fine mesh should keep anything out that could make that sort of impact, shouldn't it?