Perhaps a defect in a cable or connector such as a broken wire or a dry solder joint? These often cause problems that mysteriously appear or disappear as the cable is moved and the changing forces on the defect make and break the connection.
Nope, I tried everything, twisted the cables, etc. I even changed from power connector to another and changed SCSI cable. Outside it worked, inside didn't. Working perfectly outside, as soon it got close to the metal of the chassis it spun down, and as it got away from the metal it spun up.
