Do you have any reflux issues? Heartburn on a regular basis? It could be that this particular combination of foods is a trigger for reflux for you. Another potential trigger food is tomato. Do you have any similar issues with tomatoes or tomato products?
You take aciphex, I’m assuming you have acid reflux and aciphex successfully treats it? Perhaps it’s the hydrogenated oil in the peanut butter. You aren’t allergic to peanuts but do you have any allergies? If it’s not the oil in the peanut butter, it may be one of the other ingredients not found in whole peanuts.
Okay, let’s put our heads together: What other foods are very big on hydrogenated oil? Only one comes to my mind, and that’s margarine. Try a good-size portion of margarine on your bread and let us know what happens.
Is hydrogenated oil a component of just “processed” peanut butter from the major manufacturers, or is it a natural component? Would it be worth it to try some natural peanut butter to rule this item out???
I almost have the same situation, but it’s not a burp. More of a hiccup, sorta. But, like the OP, I can eat peanuts and not get it. I can eat a peanut butter sandwich and not get it, but if I just dig a dollop of peanut straight out of the jar and down it, I do get a weird sensation somwhere in the esophagus/stomach area. For me, though, it’s more like a hiccup that never quite makes it.