Strong Pull Sensation Behind Balls When Hanging

When hanging SD and swinging the weights in a 40 degree arc(Bib starter) or SO at my desk using a pulley, I am feeling a strong pull behind my balls near the base of the penis. Low in the structure, not upper/dorsal.

Hanging 7.5-10 lbs for 15 min sets, 15-20 min rest between sets and 1.5 hrs to 2.5 hrs total per day.

What is this I am feeling?