Kel84 Hum

[Rocky]

Hi all, as you can see I am a newbie to this forum and I am also a newbie to valve amplifiers although I have been into Hi-Fi for some 35 years.
I have just finished building a Kel84 amp that I bought some two years ago and would like to ask you experts some questions.
The mains transformer on the amp is humming quite loudly and I would like some advice on how to maybe eliminate/reduce this. There are two plastic spacers on the top and bottom of the transformer which should isolate it from the chassis but it still hums.
Secondly, I am driving Quad 10L speakers which have an sensitivity of 84dbs and 8 ohm impedance. This is not the optimum I know but the room is not too large and I get a reasonably loud sound. I am however a little worried that I may drive the amp into clipping and damage my speakers. What is the audible effect of clipping so that I may recognise it when it happens?
Thirdly, to be a pain, another question. I have a slight hearing problem in that my right ear is not as good as my left and on other amps use the balance control to adjust the output. There is no balance control on the Kel84 and was wondering if I could add a resistor somewhere in the left channel to give the same effect.
Thanks in advance for any advice forthcoming.

Allen