Possible causes for sudden , volcano like intermittent bleeding at the surgical drain site in weeks after kidney transplant ?

See surgeon ASAP: For this it's best to see your surgeon as soon as possible -- "volcano like bleeding" is an emergency. Go to er.

Old fluid collection: Drains placed in the or are usually placed through safe pathways from inside to the outside of the abdomen - rarely this may not be so. The drain was probably left in a space that was expected to collect fluid or blood and the plastic itself may have become blocked. It is possible that an internal collection of old blood +/or fluid decompresses intermittently through the pathway, see your doctor.