hey,
first i wanna say that i was not talking about a popping sound, but more of "popping" (more visible) veins due Hard Flaccid.
I'm sure that it wasn't a doppler that gave u an erection, doppler is an ultraschall. I think they gave you an injection to cause an erection, right?
Anyways i would recommend you to have an ultraschall as well to rule out scar tissue. But it is most important to relax a little. The fact that your erection got less rigid could be more of a psychological thing, might not. But try to relax. Like I said, there is different types of priapism (and we don't even know if some of us do really have a priapism type of issue!). Different types of priapism mean different affects. Especially if its is about a mild case. Priapism is usually not permanent, and causes a rigid erection for hours without any sexual stimulation.
In summarizing, we don't know if it is a priapism type of issue. We don't know what kind it would be. If it is about any type of priapism we still would not know if it can affect the penis same ways.