Was leaving work today and noticed my 93 YJ was making a whining squealing noise in 3rd an 4th gear at 2K+ RPM's only. I couldn't tell where it was coming from but maybe the back of the engine. It started out soft but got louder as RPMs increased to the point of "oh sh**" what is this!? So I pulled over to check some things and got back on the road. Well the noise stopped but an Hr later it came back so I drove it to the shop. Go figure, they couldn't replicate it so now I don't know what to think? Originally I thought maybe a TO bearing but now I'm not so sure since the noise is completely gone for now. It definitely was not a belt. Any ideas?