Sounds odd for the CPU but usually if everything else is good and you have a bad CPU you get a few dings or beeps...or something like that. I suspect that it is more related to the PSU on the MDD which are known to have problems after a few years. Usually past the Applecare warranty. Try testing the PSU with a multimeter and see if the voltages are correct. If that is good, then you may want to have a closer look at the motherboard and CPU.