Apple Cinema Display 20inch monitor

Hello,

I have a 20 inch Apple Cinema display plugged into my Mac Pro. It's about 4-5 years old. Have copied and pasted a link to show you exactly which model. http://www.hiwtc.com/photo/products/6/04/31/43178.jpg

I have noticed recently that the top of the monitor becomes incredibly hot and on close up to the metal I can almost smell overheating. It is working perfectly so no other problems than the intense heat on the top only. Is this normal? I'm not sure it is has always been like that and it's something I only recently noticed.

I look forward to hearing from you.

Thanks

Sophia