I believe I have a problem with a relay. Every thing seems to be working properly on the clock and display. When you select bake, broil convect bake etc. it shows on the display and the temperature selected also shows up. The display then switches to preheat showing 100 but does not start to heat. I can hear a slight sound like a hum/whistle that comes on approx 15 seconds then goes off for approx 5 seconds and keeps repeating this sequence. The sound seems to be coming from the back side of the oven near the top. The last couple weeks is when it started acting up. Somtimes you could only get it to heat by selecting broil. Other times convect bake wouln't work but bake would and then if you switched it to convect after it started to heat with the bake setting it would continue to work with the convect bake the rest of the cooking time. I would appreciate any advice so I know the correct part to order and how big a job it is to replace.