Tim,
Gail is absolutely correct in the potential of Cisplatin to cause permanent hearing damage but it is fairly rare. What is more likely is radiation damage to the eustacian tubes causing fluid buildup in the ear canals. That happened to most of us and it was like being underwater or your ears not popping when making a change in altitude. I suffered with that for quite a while during and post treatment until the tubes healed up and started functioning/draining again. They could see the fluid buildup on the MRI's. I had physical pain as well.

Always discuss and hearing changes with your MO. Ringing in the ears and difficulty in hearing should be reported immediately.