The causes of imbalanced testes can be:
1. Anatomical variation- there is normally a difference in the position of both the testicles, due to difference in the anatomy.
2. Varicocele- dilation of plexus of veins in the testis
3. Hydrocele- fluid accumulation in the testicular sac
In your post you have not mentioned about any history of trauma.
Under such condition, investigation like Ultra Sound
Scan of the scrotum
will be helpful in detecting any problem in the structures present in that area, including any abnormality in the blood vessels (varicocele) or fluid accumulation (hydrocele)
So, kindly meet an Urologist
& get a proper physical examination done.
Wishing a Good Health.
Thanks & take care.