computer making long beeping sounds?

Hi guys

I have no idea about computers so I thought I would ask for some help. I have been getting this police siren beeping warning sound especially when watching flash streams etc. The computer feels hot on one side but not the other. The computer is very old it only has about 500 ram in it. I think it maybe the fan or cpu which is often at 100% but i am not very knowledgeable at all. Crome is also taking up so much CPU The noise happens when i use media like flash streams.

thanks for your help

scouseman