I just replaced the Power Supply Unit and when I switched my PC on, it made a diesel engine type sound again but it only lasted about 30 seconds this time. Could it be the CPU fan because I cleaned that recently too. I only have 3 fans in my PC anyway, the CPU fan, the PSU fan and the graphics card fan. WHat can the problem be? DO I now have to buy a new CPU fan only to find it the problem will not be fixed?