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<blockquote data-quote="mm1352000" data-source="post: 878149" data-attributes="member: 82144">I would say so. If it were induction (which is the other common source of hums) then I would expect moving gear around to make a difference.&nbsp;All good things to try. I think by doing that you rule out the cable and sound card.&nbsp;Technically all it requires is a difference in impedence to earth. Or at least that is my understanding. If the grounding is poor it can also be a problem.&nbsp;Also a good check to confirm earthing issues.&nbsp;Can you or have you done the same for the amp (if relevant)?&nbsp;That is a very good check. To simplify, you could also potentially switch the PCs completely - may or may not be easier.&nbsp;iPods aren't really grounded, so not surprising to me.&nbsp;The fact that when you unplug the audio lead the problem goes away suggests that the earthing is bad in either the amp or PC. Current will be flowing from one to the other on the sheaths of the RCA connectors... that is the link. Get a decent MM if you can and measure the DC level relative to the power socket ground level on the outer part of each RCA socket with the cable unplugged. This may/should tell you whether the PC or the amp is the problem (ie. you'd expect both to be flat at 0V, but I think you'll find at least one connector that is not). Then you can take it from there.&nbsp;That's my 2c anyway. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile&nbsp; &nbsp; :)" loading="lazy" data-shortname=":)" /></blockquote>

[QUOTE="mm1352000, post: 878149, member: 82144"] I would say so. If it were induction (which is the other common source of hums) then I would expect moving gear around to make a difference. All good things to try. I think by doing that you rule out the cable and sound card. Technically all it requires is a difference in impedence to earth. Or at least that is my understanding. If the grounding is poor it can also be a problem. Also a good check to confirm earthing issues. Can you or have you done the same for the amp (if relevant)? That is a very good check. To simplify, you could also potentially switch the PCs completely - may or may not be easier. iPods aren't really grounded, so not surprising to me. The fact that when you unplug the audio lead the problem goes away suggests that the earthing is bad in either the amp or PC. Current will be flowing from one to the other on the sheaths of the RCA connectors... that is the link. Get a decent MM if you can and measure the DC level relative to the power socket ground level on the outer part of each RCA socket with the cable unplugged. This may/should tell you whether the PC or the amp is the problem (ie. you'd expect both to be flat at 0V, but I think you'll find at least one connector that is not). Then you can take it from there. That's my 2c anyway. :) [/QUOTE]

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