Do you take any medications such as propecia? Did they do a hormonal check on you (lab work to check hormone levels)? Does diabetes run in your family? Just things to look at.
I would say that many men have this scrotal tightening as part of a natural reaction and it's normal. Things like changes in temperature can influence it.
The good news is that the doctor you talked to about it wasn't concerned but I'm sure you'd like to find an answer. Let's see if anyone else responds. I'm interested too!
You are probably being told it is normal. You will read all over the internet that this happens and urologists are going to tell you that. UNLESS you have pain or are having difficulty conceiving a child due to a raised temperature of the testes, you are going to be told this happens. It's different but not a problem. It's a change but not abnormal.
But you are looking for answers. They do relate things like diabetes and even low blood sugar to this happening more frequently. Mechanism of action is something I can't explain about that but am just saying it has been correlated in the info you can find on this. The endocrine system is your hormones--- and hormones are directly related to your testes and what goes on with it. A symptom of low estrogen, yes, men have estrogen, is tight scrotum. Thyroid issues can be related as well. Overall, lab work to look for any abnormalities may be a further window into your personal situation. Otherwise, there will be nothing for anyone to go on. And you'll be told it's just normal.
So, ya, hope someone else chimes in.