Air Handler: Armstrong 40528C093
Transformer: Basler Electric BE321640GEK (photo attached) - a quick web search found it here:
Amana, Goodman Transformer 208/230 Volts 24 Volt Secondary: Best Buy Heating and Air Conditioning
(note: although that webpage shows the primary voltage as 208/230, the sticker on my transformer actually shows it as 208/240 - they both match in showing the secondary as 24V and the sticker on mine also indicates 40VA)

Blower control? / time delay module (photo attached): Heatcraft FTC8-ECO3 or Armstrong P/N 39971B001

Situation: (Note: outside unit is running properly.) Turn on thermostat and sometimes air handler blower doesn't start. When this happens, I've opened the control panel section of the air handler and a very loud hum is coming from, I presume, the transformer. I say I presume because the module listed above is right beside it so it's hard to tell which of them is producing the hum. I tried moving the blower a few times and that did NOT result in it starting up, so I am guessing it's not a dead spot. Additionally, it turns freely so apparently it's not a problem with bad bearings. Lastly, a bit of history... last summer it first started this intermittent problem. The air handler is in an attic storage area and the problem seemed to happen more often in the afternoon (so much hotter in there). I thought perhaps the transformer was overheating so I attached a spare PC CPU heatsink to it and that seemed to solve it. But now it is happening again even in the early morning when it isn't hot in there. Turned the blower motor a half turn again (it still turns freely), but still didn't start. Left off the circuit breaker for a while (half hour to an hour) and it did start after that. At this point, my best guess is the transformer is going bad, but I am definitely not an HVAC or electrical expert. Again, the transformer is immediately beside that 90 second fan off time delay (is it also a blower control?) module so I can't be certain which is the source of the hum. If it would help, I recently got a digital multimeter. I'm only just learning how to use it so I'm happy to test anything but please tell me what/how bearing in mind I'm new to it.

Thanks in advance!!