This could be a sign that your fan is going bye bye. Fans are normally
pretty quiet. When was the last time you have dusted the inside of the
tower? Betcha there's tons of dust bunnies living inside your fan. If you
are not comfortable to replace fan, take it to repair shop. Fans are
relatively cheap compared to having to buy all new componants because they
got too hot. The fans should still run during standby mode because the
motherboard is still on. First thing I learned about computer repair, make
sure you unplug the computer from the outlet because the motherboard is
still working even if the computer is off and can give you a jolt.