Slightly sour, off after taste

I'm wondering what this might be from. I have noticed it in my last two batches, a pale ale that's bottle conditioned, and a brown ale that was kegged. It's just a slightly noticeable, kind of sour, something's-not-right taste. Could this be due to high fermentation temps? Or fluctuation in temps? Anything? Please help... thanks!

How long are you waiting to taste them....and does it improve with age?

The Pale Ale has been in the bottle for four+ weeks now. And I actually only noticed it once. But it was the same off-ness I found in the kegged Brown, which has only been kegged for a week (brewed three weeks ago, so still young).

I am also researching a similar problem. I have a kegged cream ale that sort of have this but it fades more every day, so it could be something that will take care of itself. I also have a hefe that just finished ferementing and I noticed it again, but it is very young and that is most likely the problem. But both of them tested slightly low on the pH, but I am not sure what a "too low" pH is. you can watch my thread to see if anyone has any knowledge on the subject.

https://www.homebrewtalk.com/showthread.php?t=74389