I am having a strange sound coming from my furnace/ blower/ etc.. I can turn my fan on from thermostat everything is fine. I can turn on furnace and everything is fine. When I turn on the AC the blower??? is making a squealing noise. I can't seem to pin point where it is coming from. Could it be a noisy bearing on blower motor? I was thinking that, but I would think that the noise would also be present when furnace and fan were running. Thanks for any help.