I believe it could be a sign of "tricuspid regurgitation". I had the same problem and looked up on medhelp which is of no use but found about tricuspid regurgitation on more googling. I'd recommend you going to a physician for a checkup and tell him if you have any pains due to pulsating liver even heart pains.
You know I think it is??? A muscle spasm. I get this too, but it's usually when my rib kind of hurts in the back and it wraps around the front. If I sit up fast from a laying down position, the area that pusates gets tight, like a muscle would. That's what I think it is....just my humble opinion
This is so strange to be reading, because I am too experiencing this pulsating sensation in my lower righ ribs. It just started yesterday. I do have a chest cold right now that started 5 days ago. I am a fairly healthy female. Not overweight. I do not drink alcohol. I exercise off and on. My downfall is I drink probably 4 cups of coffee a day and I eat too many sweets :S. I'm really curious to what could be going on??