It is really weird the DC blocker didn't help. It could be you just have some weird transformer resonance which is better fixed mechanically.
The two key features for Furman's are LiFT and SMP. Combined they are the most cost effective noise reduction I know of. Fortunately, this comes in relatively inexpensive models.
https://amzn.to/2TzW7q1
Otherwise, advanced models add power regulation, and even balanced power for lots of $$$ though, as well as being more rack friendly.
The two key features for Furman's are LiFT and SMP. Combined they are the most cost effective noise reduction I know of. Fortunately, this comes in relatively inexpensive models.
https://amzn.to/2TzW7q1
Otherwise, advanced models add power regulation, and even balanced power for lots of $$$ though, as well as being more rack friendly.