My 3-year old Pangolin P5 has recently begun making rattling or buzzing noises that I believe are associated with a fan (certainly with *some* rotary component that's wearing out). They're coming from the left side of the case, but they do seem to be independent of the more typical fan noises I'd gotten used to before this started (I will at times hear both at once, and they seem to switch between RPM settings independently of each other). They do not seem to be as strongly correlated with CPU or GPU activity as the normal fan noises (if anything, the bad fan seems to let up when the main fan kicks in). They also do not seem to be correlated with drive activity (I had been afraid at first that the noises might be coming from the hard drive, but I'm pretty sure by now that that's not the case).
The buzzing noise usually starts when I boot the machine and immediately log in, within a minute or two of reaching the desktop, and either stops within 5 to 10 seconds, or continues until I shut the machine down (which I generally do within a minute or two to avoid stressing the malfunctioning fan further). It happens once in every five or ten boots, and rarely at any time other than shortly after boot.
The rattling noise seems to be coming from the same location and I believe it to be a lower RPM setting of the same fan. It can show up at any time and continue for a fairly long time (to the point that I'm not sure whether it's an intermittent noise, or a constant one that I only intermittently notice).
In summary: Some other fan than the main CPU fan seems to be wearing out, but I'm not really sure exactly where it is or what component it's responsible for cooling. Its activity does not seem to be strongly correlated with CPU load, and it only kicks up to high RPM within the first few minutes after boot. I'd like to figure out where it is, if I can replace it, and, if so, what part I'd need to order (as well as what the consequences would be of letting it fail completely).