trans / xfer case noise

so im hearing a noise in the transmission / tranfercase area. its a slight whinning, screeching, best described it sounds like brake squeel but not as loud.

it only happens in gear and doesnt matter what speed. ive been curbing the tires and getting on the gas to try to pin point the location by hanging out of the car. even slightly on the gas i can hear the noise. what i need to have a friend do this while i get under and find the noise, but i know this is dangerous.

so i took it into my local mechanic, they said there is vibrations in the xfer case and that i can still drive it no problem. so i drove it home and the noise was not there. now the next day, after probable 5 miles of driving the noise is back.

what can be causing this? has anyone had this issue?

thx.

ok found the cause of the sound. its not coming from the trans area. got my neighbor to help me out and it was a loose spark plug.