98whitehoe

did the nv3500 swap.have been driving it for awhile with NO problems till yesterday. we were driving it home about 55 or 60 mph and all of a sudden there was a loud buzzing or humming noise and i was like oh crap so i pulled over as quick as i could . i just knew that there was something bad wrong with the trans swap .didnt see anything so i started it back and pulled out with no problems . when it got back to 55 or 60 it done it again . we were near the hospital so i pulled in there and checked it again still nothing, by this time the wife and kids were tripping out.i sat in the parking lot puzzled.then i had my wife start it again sitting still and i waited and waited then all of a sudden the noise came again but i discovered that the starter was flying in and out or cranking on its on while the engine was running. so i turned it off again and checked the flywheel for damage and luckly there was none.so i had to figure out how to get it home.i told the wife to start it and when it started i would cut the "solonid" wire with a pocket knife and leave it running to get it home and it worked but i cant figure out whats going on. maybe the ignition switch? or a shorted out wire or the starter but it just started this all of a sudden . if anyone has had this happen before i need help troubleshooting this problem.