Second Bladder Tank sounds empty?

The deep submersible well system I have has two 200 gallon well-x-trol bladder tanks. They probably figured we needed them for 3 houses and a 3 gpm well. I am the only one using the well and have noticed ever since I started using the well 7 years ago that the second tank, furthest from the pump sounds empty when I knock on it. The first tank closest to the well has a more solid sound when you knock on it (maybe its waterlogged). I know this is not very scientific but I figure you experienced guys may be able to tell me what is going on by the sound a tank makes when you wrap on it. Tanks are 10-12 years old and I have been using the well for 7 years. The tanks have been that way since I hooked on. I know I need to drain them and check the air pressure but have not done so yet.

Yep, yer right, draining them and checking the air pressure is the only way. But knocking and getting different sounds says you need to check the air pressure.