Can Computers add noise to home electrical system

Darrylhifi - I did and it's rubbish what you read about computers causing problems in spite of dedicated lines for your audio. That would mean that your neighbours' computers and other gear as well would inflict your line because they all are sucking from the same transformer in the block. Not really. But: I used to have trouble even with my fridge coming on and causing quite some clicks while listening with gear on the same line. After installing two dedicated lines - one for the frontend and one for the amps - all that spooky stuff is over. That does NOT mean that I would not run f.e. PS-Audio PowerPlants which I do. But dedicated lines definitely are the first step to get rid of trouble caused by other gear in the household. And they are good value, too!
Thanx and good luck!

100 percent agreed. Dedicated lines first . My question was despite having dedicated lines and I appreciate your opinions .

The only question I would ask is are the fan motors AC or DC. How old is all the house wiring. Is the house ground intact ok that is more than one. I run a dedicated line with a power conditioner and have no problems.

Yup, I got 2 20amp lines and I couldn't be more pleased by the improvement. $500 bucks and it's like you upgraded everything!

I suspect computers DO add noise, despite dedicated lines. I can certainly vouch for microwave ovens adding a discernible grain to the high frequencies, dedicated lines or not! I could always tell when the microwave was still plugged in because the harmonics were stilted -- if they were there at all! And this was on two different coasts, so it sure isn't a local effect.
A dedicated line, contrary to stated opinion, does NOT eliminate interference from household lines on non-dedicated lines. Try turning off your cable box and listening to the same cut again. Or, as I suggested, the microwave. Or, your 2MHz cordless phone. It's distressing how many appliances that were not around in the 80s or even early 90s can now inject RFI or EMI into a system. If anyone knows a cure, let us all know!

Interestingly, when I had a system set up in the basement, and had a separate circuit box for the dedicated lines -- and the lines did not run through the main floor of the house, it seemed quieter. Operative word: SEEMED. There was no way to compare, although I did unplug the freezer in the basement, but that was to eliminate the freezer motor hum. I suppose I could have tested more, but that wasn't the point at the time.
Do the microwave test and see for yourself.