Folks, here's an update on my earlier posting.
Previously, I advised attaching a vacuum cleaner to clean dirt and dust out of our Surface Pro. That's what I did on the advice of an expert on PC maintenance. It helped, but didn't entirely cure the problem.
Today, about a year on, my Surface Pro still has some fan noise on occasion, but the good news is that the fans have mostly quietened down. I only get the worn fan bearings noise every now and again.
However, my concern was whether the fans were still doing their job. Well, a bit of research has revealed that the i5 processor should operate at a core temperature between 40 and 80°C. If it exceeds these parameters (bearing in mind the maximum temperature for the i5 processor is 100°C) then your Surface Pro should automatically shut itself down, with a warning message to tell you what's happening, and not permit a restart until a safe temperature is reached. So you should be safe, even if the fans aren't doing their job.
Tonight, my Surface Pro was getting hot while I was playing a video. I had the idea to find a core temperature monitor that'd confirm how hot the Surface Pro was getting. I downloaded the Open Hardware Monitor. This has confirmed that both i5 cores were operating at around 60°C, well within normal operating parameters. So, if you're concerned about overheating, I suggest you download a core temperature monitor.
One last thing. Some of these monitors will (apparently) also give information on fan speeds. I've not yet found how to do this. If you find out how, then please post a reply.
In summary. Your fans will probably get quieter over time. Do clean your cooling ducts with a vacuum cleaner, and keep an eye on cooling with a core temperature monitor downloaded from the Internet. In any case, fear little, as your Surface Pro's self-protection features mean it will automatically shut itself down if it's in danger of reaching an unsafe temperature.
Hope this is helpful,
Rick.
(A professional in the computer industry)