It almost feels like muscle spasms, but it is underneath the muscle. In comparison, my left side is a little stiffer when pressing than my right. The pulsating is worse when sitting. It has started to have a dull pain over the past 2 hours.
I am 27, 228 lbs, in very good health.
Sorry for the confusion. It is almost directly on my left side. Between the abdomen and the back. If you make a C shape with your hand and place it above the hip bone, thumb to the back, it covers the area from tip of thumb to tip of mid knuckles on fingers. Height is width of hand.