Hi Rob,
Welcome to Beoworld !
First check that the mains voltage setting (at the bottom of the Beomaster) is correct for your area.
Some Beomaster 1900's are prone to hum a bit if the supplied mains voltage is a bit on the low side.
If f.e. you live in a 230V area and the Beomaster is set for 240V - if it hums set it to 220V. It will not be damaged
by on overvoltage of 10V. Just remember to ALWAYS unplug from mains when setting the mains voltage.
Having said that; The humming, from your description, sounds like aging capacitors indeed.
A cap kit is available (from me) for convenience, it's huge kit with more than 60 components and I would recommend
you replace the lot.
There can be other reasons for a Beomaster 1900 (/2400) to hum, like a rectifier fault, bad voltage regulation or a
wrong power supply load, wrong wattage panel lamps etc. (a lamp kit is also available) but the hum pattern you
experience screams capacitors.
Martin