My hum was only when the fm transmitter was off.
To combat hums and buzzes in any sound related system:
- try to keep all items connected to the same power phase. Same power strip is even better.
- use good quality cables
- try to make sure none of the volume settings are too low or too high. Noise is usually introduced at a constant level at every stage in any system. If the volume setting is too low at any point in the chain, that provides an opportunity for the signal to noise ratio to lean more towards the noise - which will be amplified in later gain stages. Also, Most amps get noisy if pushed past 80%.
RM