Thanks again, all, for the replies. A few responses:
The majority of my brewing has used Brewer's Best kits. They all include Nottingham dry yeast (and I would assume the same type). I've both made yeast slurries as well as dry pitching and have gotten the "off" taste via both methods. For the would-be pumpkin porter I just finished bottle conditioning, I tried to go out out of the box. My base was the "Sparrow Hawk Porter" recipe from Papazian's "Joy of Home Brewing" and some ingredients from an all-grain recipe for "Ray Spangler's Pumpkin Spice Beer" in Mosher's "Radical Brewing" (full details at the end of this). The yeast wasn't specified for either recipe and the homebrew shop gave me Nottingham dry yeast (I asked for dry, but didn't specify the brand).
I've read a couple of other posts elsewhere about homebrewer's using Brewer's Best kits and getting the same taste across several different types of kits and repliers were pointing to the yeast. They recommended getting a liquid yeast specific to the type of beer and using White Labs and Wyeast. Perhaps a change in yeast is in order to see if that makes a difference? Do others have thoughts on the pros and cons of Nottingham?
Additionally, it seems that, regardless of whether this is the source of my "taste," that I'm fermenting at too high of temps. I don't have an extra fridge that I can control the temp on (especially not up as high as the 60s degree-wise) so what do other homebrewer's do to control fermenting temperatures?
I almost certainly have not been rinsing the B-Brite correctly so I can all but guarantee that I've left a chemical residue on my equipment and in my bottles. This no doubt is affecting overall flavor somewhere. I'm frankly surprised that the homebrew shop owner recommended B-Brite over Star Sans since Star Sans is clearly easier (and more appropriate?) to use.
I'm pretty confident that water is not the culprit. As I mentioned I've used bottled drinking water from the grocery store predominantly but also Britta-filtered tap water. At times I've gotten the taste with both sources and at other times I've not gotten it (early on in my first couple batches) with both sources.
So I've got a few variables to test out. I'm definitely switching sanitizer and I'll try switching the yeast for my next batch. If it solves the problem I won't know which was the culprit but I'm OK with that. I'll have to figure out ways to get my fermenting temp down so welcome ideas for that. I'll be happy no matter what so long as my beer goes back to tasting only like beer and not beer with some weird fore/aftertaste.
Have a great Thanksgiving!
Sparrow Hawk Porter
4.5 lbs. German light malt extract syrup
3.3 lbs. plain dark malt extract syrup
1/2 lb. black patent malt
1 1/2 oz. Northern Brewer hops
1 oz. Tettnanger hops
3/4 c. corn sugar
From Ray Spangler's Pumpkin Spice Beer:
3 lbs. raw pumpkin (fresh canned, baked for 90 mins. and smashed up)
At end of boil:
0.5 oz crushed coriander, 0.25 oz. allspice, 0.5 tsp of pumpkin spice, cinnamon, and nutmeg. Then added 0.5 oz whole coriander to the secondary.