What Causes Trembling Sensation Inside The Chest?

I am in menopause for 4 years now and last June i had a panic attack and around that time i started to have sensation of trembling inside my chest. I say sensation because nobody can fell these trembling, even not my doctor with the stethoscope. These trembling are "all the time" but when i move it doesn't really bother me, although they are there. But when i sit to eat, watch TV, or go to bed...it is very annoying. I listen relaxation music every night to relax. Sometimes it wakes me up at night and have had time to fal asleep again. I have had blood work done several time; they only find that i am vitamin D deficient and take supplement since October, but still trembling. I started hormone (patches) 3 weeks ago to see if this would solve my problem...not as of now anyway. My husband and I are retired...this can't be stress !!! Any help would be very appreciated.