What Causes Palpitations After Drinking Orange Juice Or Eating Saltine Crackers?

I just noticed a few weeks ago that when I drink regular OJ, I get heart palpitations, or racing of my heart, for a short period, like a 1/2 hour to an hour. I thought it may be the sugar, so I switched to Tropicana Lgt.,,with half the sugar of the regular. It stopped for a long period, now it's back! It also does this when I eat certain saltine crackers as well....the regular kind. Why is this? I have just turned 64 yrs. old, quite active and in pretty good shape; total chol is 164 at last reading..last year it was 253, then I started to modify my diet and it went down to 203. Dr. still wasn't satisfied, so I was put on Pravastatin, and he requests I still take the meds to keep it down; bp tends to elevate with the foods I eat (and trying to steer from), so I am on a 20mg. water pill; wt. is 157-160 lbs. 5'3". I am now in the process of exercising to help lose some lbs. Could this be a factor? Sometimes it is quite scary to actually FEEL your heart beating so fast and so hard! As long as I steer away from these two foods, I am okay and I feel just fine!