If the problem is only in engaging in second or a noise when you're in second, it must be a possibility that your second sprocket is worn out. Does it look worn? And when you say 2nd, you do mean your second-biggest sprocket, do you? It's rare for that to wear out first - it's usually the smallest sprockets that wear out first.
I would also check the chain for wear. Put a ruler along it and look to see how the length of 24 links compares to 12". If it's more than 12 1/8" then the chain needs replacing, irrespective of anything else. Even if it's 12 1/8" and you're having trouble, then it must be suspect along with the cassette.
I would also check the chain for wear. Put a ruler along it and look to see how the length of 24 links compares to 12". If it's more than 12 1/8" then the chain needs replacing, irrespective of anything else. Even if it's 12 1/8" and you're having trouble, then it must be suspect along with the cassette.