Clutch/transmission

I have a 98 freightliner century class with a super 10 in it. I'm experiencing a disturbing sound that seems to be coming from the area of the transmission. Its like a strong raking or banging sound that almost makes me think its not going all the way in gear. This only happens in the low range and mostly in 5th/6th. It also does this in reverse sometimes. But this never happens at all in high range, 7-10. If the truck has been running for a while it seems to only do it while using the clutch. If the truck hasn't been running long it seems to do it occasionally when I float also. If I'm using the clutch it can start when I transition to a gear and come off the clutch. Sometimes it will subside after a split second. If it continues I take it out and try again. It doesn't do this everytime so I have continued to work. It doesn't seem to matter if I'm bobtailing or have a load. I have had several mechanics and drivers listen and look and all are unaware of what it could be. I needed a clutch adjustment and got that but it didn't help. So now I am having the transmission pulled to get a good look inside. Any ideas?

 

I'm not sure. But they finally got the transmission out and the front looked fine. The clutch definitely needed to be replaced but we don't think the clutch was doing it or it would be all the time. Having the transmission sent to a tranny shop to have the back of it inspected.