Graphics card help?

hi all i have nvidia geforce 5500 fx agp graphics card in my pc works perfect,i bought an asus v9999gt geforce 6800 gtcard of ebay,when i take out old card and put in new one as soon as switch it on there is a very high pitched noise comes from my pc,i dont think it is coming from the graphics card itself,any ideas what it could be,i have the old card back in for now,could it be a power supply problem???or something similiar please help!!!