Know of a "Dirt Cheap" tweak?

Take some Blue Tac or some similar putty and make a small ball with it and put it under the edges of various circuit boards in our electronic equipment.. This sort of adds vibration control and damping and can be easily removed.

Read.

Putting digital and power on two seperate ac circuits makes a difference.

If your home has a crawl space or basement, placing supplemental support by way of jacks under the floor where your equipment rack, your speakers and subwoofer(s), if you have, are, will clean up the sound, especially the bass in my case (Vandersteen 2wq). Tightening  up the vibes thru the floor really cleans it all up. Did the laundry room at the same time  to even greater reduction in noise and transferred vibrations. And to a pleased wife.  I have a crawl space that runs from 3 ½ to 4 ft high. My jacks  from Home Depot ran up to 3 ft adjustible placing 4jacks, two with 4x6 beams across the spans between joists, and the other two just straight onto the joists. Total 4 hours start to finish and about $150. Home Depot had everything. Jacks ordered online and delivered. 

Completely agree with Kavakat1. Reinforcing my subfloor from beneath the crawlspace has been on my to-do list for some time now. Finally got around to it a few weeks back. I'm very pleased with the results. I cemmented 3 pillar blocks with 4X4 attached to the joists. Additionally I reinforced the joists by screwing 2X4 on each side butted up to the subfloor. Maybe overkill, but now my system sits on a much more solid foundation, close to a solid slab of concrete. Total cost was approx $200 in materials and 8 hrs. of labor.