It's simply adding a washer to the rubber isolators that hold the compressor, making the dampening slightly firmer. The noise was a higher pitched tingle sort of sound that's somewhat common with A/C units. In the pic, note the extra 1/4" washer added under the spring clip. There are three rubber isolators, which are easy to see with the cover off.
Although the noise was from compressor movement, it was the suction line tubing being too close to a threaded rod that was making intermittent vibration contact. In the pic above, it's the larger copper tubing at the upper right.
Bending the tubing slightly for more clearance is the easier and better fix, but combined with the added washers in the first post it sounds smooth, mostly just air flow noise. Inside the Scamp, it's even hard to tell when the compressor starts and stops now.