Weird taste

So my bottles have been conditioning since 12/11. It was the Brewers Best Pumpkin Spice Porter. I decided to try one tonight. Going into bottles it tasted OK. Not great, not bad either. I followed the instructions to the letter from the kit. So I figured Id try one tonight. I was met with a smell and taste that I think of as plastic. I may be wrong, but that's what it seems like to me. It did not have this taste or smell going into the bottles. I am curious what this could be? Of course I will wait a few more weeks and sample another bottle. I tried 2 different bottles tonight just to make sure it wasn't just the one bottle. I used bottled water for this batch. It was my first ever. My second is two weeks in primary and was tap water. Getting ready to bottle soon. Just want to avoid this again if I can. Thanks

Also I used an auto siphon. I ran hot PBW through it. Then a ton of hot water. Finally Starsan before I siphoned the beer into the bottling bucket and to the bottles.

One of the possible causes for a plasticy flavour in your brew could be attributable to chlorine or chloramine in the water you used for/in the brew, even from smaller trace amounts from topping up with tap water or making sanitiser with chlorine/chloramine contaminated tap water.

The flavour gets stronger the longer it sits, which could explain no hint at time of bottling but becoming apparent now.

Chlorine can be dissipated from the water just by leaving a container of water open so the gas diffuses. Chloramine is more stubborn and the most common way to deal with it seems to be using campden tablets.

The only tap water I used was for the starsan. The rest was bottled spring water. That's why I wasn't sure what would cause this.