Well I have one batch that wasn't degassed properly and understand what that does to the flavor but that isn't the issue I believe. I got a bottle from another guy I work with that is making homemade wine. It also has the same after taste to it. Maybe its a home made wine thing.?
Kit wines can have a pretty serious after taste until they age out some, especially reds. Of course any young, green wine is also gong to have a green, tart taste for awhile. That "kit taste" and/or the green taste will eventually subside.
About CO2, if it is present in a wine, it not only masks the flavor, it also seriously masks the aroma. Do try decanting a kit wine, especially if it still has too much CO2. The aroma will improve a lot.
As the wine sets in the decanter, the aroma will get stronger and better with each passing hour. Once the aroma is full, the wine is ready to drink.
If I have CO2, I slosh the wine around in the decanter about every 30 minutes. I have one early batch, which didn't degas well, that can stay in the decanter 8 hours before it starts coming around.
I like IBGLOWIN's suggestion to open a bottle, take a glass out, push the cork back in to seal the bottle, let it set 24 hours or so, then re-open and drink. It really works, with kit wines especially.