A buzzing sounds is often attributed to a failing compositor or transformer, which forms part of the electrical circuit.
Does the noise go away or is it constant, and if you tap the unit does it go away\get quieter?
Good afternoon Betty, further to our brief call I suggest you use DIA on 01983 212721 based in Newport.
They take calls between 9am and noon, so have missed them for the day but they come highly recommended.
Should they not be able to come out this week then you can try Jerry on 01983 865665, he charges £40 call out, and is available this week.