The muscle contractions you feel is muscle fasciculation or muscle twitch. Twitching is caused by minor muscle contractions in one particular area, or the persistent and uncontrolled twitching of a muscle group in a distribution of a single nerve fiber or filament. Usually they are benign and resolve on their own, but persistent flutter may need following investigations;
1) electromyography (EMG)
2) nerve conduction velocity (NCV)
3) blood electrolytes like calcium, magnesium, potassium, sodium, etc
4) thyroid and parathyroid function tests
5) blood chemistry and complete metabolic profile
The common causes can be;
1) Idiopathic; no cause is ascertained and majority falls in this group.
2) Increased caffeine intake
3) Increased alcohol intake
5) Deficiency in diet and nutrients / minerals
6) Some neurological diseases; quite uncommon
Please feel free for your follow up questions.