Power at 1.5A 12V seems like it might not drive a 1meter fan either...
Good call with the foil inside the tubes, wouldn't have thought of the static build-up with the rubber. Also, it's not a mod without duck-tape!
With the card itself, the vented holes in the PCB, is there much airflow coming through them? It might be worth blocking the ports off, that way you maximise the amount of air pushed through the card.
In terms of noise, really not a lot you can do. Those fans run loud for a reason, due to the 1U form factor and the huge amounts of air they need to push. If the PWM isn't working as intended, you may need to use either dedicated fan controller with high power output, or fit diodes/resistors to the cables and reduce the voltage.
As for being unable to read temps from the card via software, I'm thinking a third-party app will be required. Now since this is Linux you are dealing with, I'm uncertain as to what's available. A quick search gave me lm_sensors and a front-end xsensors. Though I'm uncertain if they need compiling etc.
As for further improvements to your setup without going water... let's see. First and foremost, I think air filters will be a requirement, just to prevent headaches down the line. I don't know what mounts you are using at the moment, but you could try some vibration reduction with something like these...
Need to figure out a replacement to the rubber tubing; It's practical to test, but I'm not sure about long-term. Could get some PVC or ABS ducting conduit if you don't need the flexibility. Or a vacuum cleaner hose, preferably one with a smooth interior to minimise drag. There are car radiator pipes too with smooth interiors, but I'm not sure about anti-static qualities.
You could buy some sheet plastic and glue together a custom duct yourself, depends how far down the DIY hole you want to go. Oh the modding bug, how I miss thee...
In the number-crunch software I use, when the GPU is loaded the host CPU cores run about a total of 25%. When the host CPU is loaded which happens when the problem will not fit in the memory of the GPU, the GPU is 0% utilization ... is at idle in other words.
Also, in the thread starter post, I mentioned that the C2070 that I have idles at ~83 deg C or did until I started using the MSI utility. I could not figure out the Nvidia utility. The point is, is that the GPU always needs some cooling. In the MSI utility a fan speed vs GPU temp control curve can be setup very easily. At 50 deg C the fan is at 50%, 80 deg the fan is at 80%. At 90 deg C it is at 100%. However, the temp never gets above 83 or 84 deg at 100% GPU. At idle it is 61 or 62 deg C with the integrated fan slightly noticeable There are ~15 fans altogether in 3 computers. But now I can be on the phone & no one accuses me of being a beauty salon.
The noise you are experiencing I used to have a few years ago with a few Delta fans in different machines I had at the time. People I phoned from my office thought I was blow drying my hair! NOT!
This is what put me on the water cooling path. I have much quieter fans now. On the radiators they are push/pull with filters. I would like to have a little more sophisticated control of the fans in the computers just to slow dust accumulation, but the filters help keep the dust out of the radiators. Elsewhere on this forum I posted a few pics of a totally plugged radiator. Disgusting, I thought Rob was going to ban me for posting those pics!
With Ubuntu you might consider an electronic fan controller like this Zalman. I tried one of these out sometime ago but not that exact one. That link is just the 1st link I just now found for the example. The one I had used 8 thermistors and of course I tried to use all eight just to monitor temps with only 2 or 3 fans being controlled. It worked quite well, but all of that extra wiring made the inside of the case a real rats nest. But, when things warmed up the Deltas would come up to speed very nicely. So I made my phone calls when the CPU were not doing much.