Plastic taste and stressed yeast

I know that fermenting at very warm temperatures can cause yeast to throw phenols. The room I use for fermentation has been sitting at 64°F with ferm temps going no higher than 68°F yet I'm getting a very distinct plastic taste and smell from some of my beers. I'm currently fermenting some beers that I've added Potassium metabasulfite to drop out Chlorine/Chloramine to see if that's the culprit. What I'd like to know is under-oxygenating my wort causing the yeast to stress and throw phenols. None of my beers are over 1.050 SG and I typically splash the wort around a few moments to aerate it.

What yeast strain(s) are you using?

I've used Wyeast Northwest Ale, S-04, $ Wyeast 1084.

i have a beer that had the plastic taste using the NW yeast. I'm convinced it's there but no one seems to be able to smell it. I think I have narrowed it down to using braided PVC tubing at boiling temps when it's only rated to 155 degrees. I've changed water and tubing on my last batch so hopefully I'll have some answers in a couple of weeks.

I have always attributed my plastic taste to pouring of hot wort into a plastic fermenter.