About two days ago i started to pick up a persistent taste in my mouth. has localized behind both top molars as a sour taste ?

Sour taste: Bacteria growing in mouth can sometimes cause sour or foul odor. I agree with earlier recommendation to be checked to rule out infection of teeth/ gums.

Sour taste: Could be poor plaque control, food impaction, which is easily remedied or more serious conditions such as periodontal disease (gum infection), periodontal abscess or tooth abscess. Get it checked out asap at your dentist, before you have bigger issues, more grief and a bigger expense.

Lots: Lots of possibilities including, but not limited to, dental infection, gum infection, impacted food, infected tonsils/adenoids, sinus infection GERD. See your Dentist. Let him/her find the cause and provide the appropriate treatment.

Have a dentist: check for gum or tooth infection or tooth cavities.

Sour = Acid: Acid indicative of infection. Without an examination with radiographs, it is impossible to tell if you have a periodontal issue, a draining abscess, or even a sinus infection. Please see a local dentist to rule out any dental issues.