Oh yeah, hadn't thought of that one
Other things to try;
copper, silver plated copper, silver, silver alloy wiring or two plastic cups with string between ?
position of moon when building something
mains cables & plugs
remove the pcb's from everything and use point to point
series v shunt regulators or super duper regulators
bulk foil resistors v standard metal film
film caps v electro v tantalum (wet & solid) v PIO v polypropylelne
volume pots v stepped attenuators
active v passive pre,
EI v toroid v R core v C core
standard bridge rectifier v schottky v fast recovery
plain capacitor smoothing or CLC or CRC .... or CLCRC ?
hard wiring everything in sight
the whole earthing thing
soft start or not
speaker protection or not
complimentary or quasi complimentary AB or class A or class D , bipolar, mosfet
resistor or diode or transistor biasing
to protect amp output or not - zobel, inductor
to filter the input stage or not
powered by farmyard muck ?
current mirrors ?
I could go on..............