91 Mirage: Clicking/grinding noise from gearbox in 3rd gear

I bought a 91 Mirage a few months ago when I found myself unexpectedly in need of a 2nd car ASAP. I bought it cheap and I got what I paid for...it's a real beater. It already made plenty of noises while it drives, most notably a grinding noise in the transmission. But hey, it runs.

However, in the past few days, a new noise has started. It sounds like some kind of metal clicking or grinding against something else. The noise sounds like it is coming from the gear box...almost like it's just under the leather stickshift boot. And it ONLY happens in 3rd gear.

Any ideas what this could be? In case it wasn't obvious from my description above, I am not a car guy, so please be gentle. Heh.

Thanks in advance.