This sounds like the Input Shaft Bearing in your tranny.
You may what to check and make sure you have enough fluid.

If it is your tranny you will notice that 5th gear maybe the loudest and 4th gear may be the quietest.

Do a quick search on input shaft bearing or tranny rebuild.
Here is a link to a D.I.Y. rebuild.

Tranny rebuild

Good luck....

1991 FJ 80 Land Cruiser for fun.
1998 GS300 for the wife
1998 GS400 for me
1991 Supra SOLD
1986 4Runner 335k miles-22re EB inside.SOLD