I'm not sure what to make of it, but I have very little knowledge diagnosing transmissions. I have a 95 Del Sol with the stock d15b7 and matching transmission. So far, I've had no trouble with pop outs, finding gears or even grinding. However, when in gear, usually 1st-3rd, there is some sort of grinding noise. Can anyone make any sense of it? I'm sure its probably obvious to someone.

 

A bad mainshaft bearing is very common on this transmission. See if it makes noise in neutral (at a stop) with the clutch out and the noise goes away when the pedal is depressed. If it does, it is the bearing.

 

How detrimental is this? Is the transmission on it's way out or will it just make the noise for the remainder that I keep it?

 

If it's the input bearing on the mainshaft, the seal will start leaking, and eventually the trans will self destruct.