The fluttering or vibrating feeling sensation comes from an abnormal fast tiny muscle movement or twitch called fasciculations. Fasciculations happen when chemicals released by the nerves that stimulate muscles to move are released to excess which stimulates muscles to move fast.
Sometimes fasciculations can be seen if they involve a large "muscle unit" that is supplied by an abnormal nerve and they are close to the skin surface.
In the penis, muscles are very small and thin and are supplied by many tiny nerve branches, so while fasciculaitons there can be felt, they cannot be seen.
Now, fasciculations can be benign or pathological, i.e associated with disease.
In both cases they can happen in any area of the body - face, ear, arms, legs, trunk, genitals, legs, etc. Usually the pathological ones are visible, involve skeletal muscles and are associated with other neurological symptoms.
If your prostate exam and PSA are normal, it is very good news. The cold feeling in parts of the body can be produced by abnormalities in nerves and blood flow. Sensory nerves may send messages to the brain when there is nothing cold or warm touching the tissues.
The good news is that special nerves that cause erection and ejaculations are working well. The coldness in the prostate area and the "flutter" that is hard to localise in the penis are most likely benign.
I understand this type of sensation can be worrisome and annoying. I also had female patients complaining of fluttering feeling in their genital and pubic bone area which lasted on and off anywhere from 1 week to several months. They were otherwise healthy and the feeling eventually went away.
It sounds like all important tests were OK. If you have any reason to think that you have been exposed to any sexually transmitted infections in the past, it would probably be prudent to check for evidence of antibodies
in your blood if it has not been done already, just to be safe.
I am quite certain that this is a self-limited problem and will resolve with time.