PC is working slow and sound problem

Hi,
When I am copying the files & I start my (vlc & mpc player), then little noise from my speaker like “ex.ttttttrrrrrrrrrrrrraaaaaaaaaaannnnnnnnnnngggggggggg” comes out. And also my win 7 loading is very slow. & also my games are hanging on every minute.
Some people told me it was a dust problem. I used updated antivirus and run disk cleaner delete temporary and recent file and logs. Some these problems do not appear when I changed the SATA cable, but some time it also appears even changing the SATA cable.I can’t understand what is the problem.
Please help me.
