It might be due to the fact that there is a Suzuki badge on the front of your vehicle.
Seriously though, every suzuki i've ever had has had either tranny or t-case noise. I always believe it to be the tranny making all the noise, but as long as it still works (which it always still has), then i just keep going.
I think the actual 5th gear is a different type of cut to the others and just produces a different noise, but that's just my opinion.