Nissan Repair: First three gears sound funny.., shaft bearings, input shaft

Question
Hello sir,

I recently purchased a 1993 Nissan Pickup and I've noticed that while it's in first, second or third gear, it kind of makes a knocking sound that is pretty muych synched up with the rpm's but when i shift into 4th or 5th gear, it sounds just fine, no knocking.  I know that I will have to replace the clutch soon because it's almost gone, could the clutch have anything to do with this? Do you think I am hurting the truck by driving it?  Any information would be greatly appreciated.

Thanks!

Answer
Mike,

I would replace the clutch if it is as loose as you say.  But, the noise with the transmission would not be related since it is only in the first three gears.  If it were first and second I would think internal damage to the transmission.  I would change the fluid and see if it improves.  I had one where the input shaft bearings were going out and a fluid change gave me another two years before I had to take it apart and change that bearing.