To help assess the root-cause, some more information would be useful:
1. Is the RFI only on 160M? If not, does the noise level decrease with frequency? Is the RFI constant across all bands?
2. A time-domain assessment would be helpful. You can obtain this by using the audio scope feature of the radio. Change the mode to AM and measure the waveform pulse-to-pulse interval (assuming it's an arc-fault noise source). If the intra-pulse time is 8.3mS, then the source is, most likely, a 60Hz spark-gap noise source.
Perhaps, if you can post a time-domain picture for 160M and, say 20M, that would be useful. That waveform will help delineate the source possibilities.
(disclaimer - I don't own the IC7610 so I am assuming it has an audio-scope feature).