What you need to do is invest anything from $3 to $15 in a tool called a "Mechanic's Stethoscope".
A mechanic's stethoscope is similar to a doctor's stethoscope, but it works in a different way. Because sound is no more than rapid variations of air pressure caused by physical movement of objects, a mechanical stethoscope has a metal "probe" which you touch to any part of a machine that you suspect of causing a noise. When you touch the probe to the part that's vibrating to cause the noise, the probe will also vibrate just as the part causing the noise will. The vibration of the probe causes a diaphragm in the stethoscope to vibrate, causing you to hear the same noise, but much louder, in the earphones of the stethoscope. Thus, you locate the source of the noise by touching the probe to the place on the machine where you hear the noise the loudest through the stethoscope.
A mechanic's stethoscope will typically cost $15 for one made in the Good Ole USA to $3 to $6 for the same thing made in the Good Ole People's Republic. I've been fixing appliances for over 20 years, and having a mechanic's stethoscope to pinpoint the source of a noise is a "must have" tool so far as I'm concerned.
I expect that if you were to touch the probe to the transformer in the top left corner of your your "silver box", you'd find that it's the source of the noise. Look for any screws holding that transformer down, and see if they're loose. If there are not screws, jam a toothpick under it to prevent it from rattling against that box metal.
This place sells both the KD Tools and Lisle mechanic's stethoscope, both of which sell for about $15:
KD and Lisle are automotive tool makers that have been around since I was a kid.
This place sells a similar thing, but probably made offshore for $2.25:
and, Harbour Freight sells that same $2.25 stethoscope for $6:
I expect they'd all work equally well. Every DIY'er should have a mechanic's stethoscope to pinpoint the source of a noise. Without one, it's like trying to detect the source of a smell.