@erik_squires, I would not expect galvanic isolation in a low end DAC. There is a definite cost in doing it, especially if the DAC is USB powered. If externally powered, there is less justification, but it is still there, especially if you want to support USB2.0 data rates.
If you are powering off a laptop, one quick test is to unplug the power cord and run off batteries. In some cases this can significantly reduce noise. With the power cord connected, there is a high frequency noise path. It is assumed it is the noisy USB supply that is the issue, but as likely it is noise on the AC supply transmitted through the USB ground connection. Sometimes pulling the ground pin on the AC works, sometimes it does not. Relatively low cost ($200) medical grade isolation transformers work well. They are designed for low leakage, hence have shield windings.
Something like this: https://assets.tripplite.com/product-pdfs/en/is250hg.pdf
If you are powering off a laptop, one quick test is to unplug the power cord and run off batteries. In some cases this can significantly reduce noise. With the power cord connected, there is a high frequency noise path. It is assumed it is the noisy USB supply that is the issue, but as likely it is noise on the AC supply transmitted through the USB ground connection. Sometimes pulling the ground pin on the AC works, sometimes it does not. Relatively low cost ($200) medical grade isolation transformers work well. They are designed for low leakage, hence have shield windings.
Something like this: https://assets.tripplite.com/product-pdfs/en/is250hg.pdf