...it's a little hard to tell from reading the thread, but it sounds like you had noise with a new chain on the smallest sprocket in the rear, which you fixed by putting a used chain back on the bike.

That sorta sounds like wear on the small sprocket. Your fix is fine if you're happy with it, but eventually as the chain continues to lengthen through wear, you start to wear the teeth on the chainwheels up front, which are a lot more expensive to replace than your cog cluster or freewheel in back. I would probably just ride with the new chain and stay off that small cog until I could get a replacement......if that's really what's going on.

You didn't give any measurement of the stretch in the used chain, which will tell you a lot more than my guesswork.