Yeah, it's most likely your atty. My question is, do you do the routine maintenance on it (ie. blowing out the
e-liquid in the atty or dry-burning)? If you do, then it's a possibility that the wicking may be burnt, which I've read gives a bad taste. Cleaning that would either mean removing the wick under the metal bridge (which I wouldn't recommend until you've read up on it), or doing the tedious process of doing an alcohol/cola/hot water soak.
Again, I would read up on these because they aren't confirmed, but more of a "trial and error" effort conducted by other members.
If all else fails, I'd just switch on a new atty.
EDIT: I forgot to ask, do you use cartridges or do you drip with your own e-
juice (maybe both)? If your filler is brownish, that could be contributing to the taste. Another thing that has happened to me is my filler doesn't connect well with the bridge/wick, giving me a dryburn taste. Lastly, the spacing inbetween each hit can determine the taste.
There's just so much that can be the cause :[