Heat Pumps and Electric Heating - Air Hanler Control Box Hum

I recently had a Trane Xr12 5 Ton Heat Pump - complete system- installed in my home. I noticed a low pitch humm, or buzz coming from the fan control box inside the air handler. The noise in constant, provided the power is on, doesn't matter if I have the thermostat turned on, or off. I see inside the box there are a couple of things that look like transformers etc. Not sure if the noise is coming from there. Is this something I should be worried about? The system seems to bd running normally otherwise. One other question, the outdoor unit seems to turn on rather abruptly, or loudly much more so than my previous, albeit smaller unit. But after the intitial kick in, it runs very quietly. Perhaps something I should have looked at?
Thanks!

Very high probability it's the transformer. Shouldn't hurt anything but wouldn't be a bad idea to get the installer out to look at it. They should be able to quiet it down or replace it with a new one.