Those don't look like high temps to me. And if the diagnostics don't say the fan(s) has failed, I wouldn't be worried. Did you move the PC right before the rattle stopped? Sometimes cases rattle/vibrate and even a small move might stop the noise. Did you install any new hardware or change a cable? You could always install something like Speccy (free) and configure it to load at boot and put its icon in the notification area of your taskbar showing CPU (or another temp) all the time. Then just mouse over that icon and a bubble pops up showing all the other temps being monitored.  
Inspiron 660s, Windows 10, Radeon graphics card.  Have been trying to diagnose a fan problem. Dell online diagnostic tests, Quick (10 mins) and Complete (40 mins+), never stop "testing" after 30 minutes and 5.5 hours respectively; and neither ever returns results.  Have run built-in self test and it says CPU fan OK. Speeds 878 rpm to 1261 rpm, thermal sensors: CPU Internal 33C to 51C; CPU External 21C to 37C; Chipset 21C to 46C.  I don't know if those are in normal range. I worry about the fan(s) and overheating because it was running noisy and rattling for many months (with OK BIST results) and suddenly became quiet while computer in use.  Why?  I'd like to replace the fan if necessary.
Inspiron 660s online diagnostic tests and fan problems