Suggestions:
Put the original pre-amp back into the chain - Is the noise present?
If so - most likely the amp
If not - most likely the new pre-amp
If the original pre-amp is not available try this -
switch the interconnects at the amplifier end only (ie right to left input and left to right input)
Is the noise present in either channel? - if not, could be a grounding issue with the interconnect.
Is the noise in the left channel? - if so, most likely the amp.
Is the noise in the right channel - if so, most likely the pre-amp.
Hope this helps
Put the original pre-amp back into the chain - Is the noise present?
If so - most likely the amp
If not - most likely the new pre-amp
If the original pre-amp is not available try this -
switch the interconnects at the amplifier end only (ie right to left input and left to right input)
Is the noise present in either channel? - if not, could be a grounding issue with the interconnect.
Is the noise in the left channel? - if so, most likely the amp.
Is the noise in the right channel - if so, most likely the pre-amp.
Hope this helps