A bump when changing sources could be a poorly designed or miswired source selector switch.
Bleedthrough is avoidable, if the manufacturer shields the input wiring and uses a high quality source switch with low crosstalk.
Some preamps go to the extreme of shorting unused inputs, so that there is zero, nada bleedthrough.
It seems that your preamp has design or wiring issues. I suggest an exchange or return, unless it is a 200 dollar unit...then those problems are to be expected.
Bleedthrough is avoidable, if the manufacturer shields the input wiring and uses a high quality source switch with low crosstalk.
Some preamps go to the extreme of shorting unused inputs, so that there is zero, nada bleedthrough.
It seems that your preamp has design or wiring issues. I suggest an exchange or return, unless it is a 200 dollar unit...then those problems are to be expected.