It's very likely that your saliva is reacting to the flavored artificial casings of many aromatic tobaccos. There are some aromatics with natural flavorants, but they are usually only available from a few hand blenders, who are rapidly disappearing. I suggest trying a combination of black and gold uncased cavendish. You'll have to search a bit for cavendish that is not aromatic, but you'll find that it's a good place to start for a cool, non-biting tobacco. Then you'll move on to the Virginia, oriental, perique, Turkish, latakia blends. Spend a few bucks on a decent pipe. It makes a difference.