Try tilting your Surface Pro to horizontal then upright. If the noise level changes, then the fan blades are moving on their bearings or something inside there (dust) is moving. I found that my Surface Pro was silent in the upright position and making a noise like the fan blade was touching something in the horizontal position.
I found that giving the chassis a few old fashioned bangs, while holding in the quiet upright position, dislodged whatever the fan was touching, and I'm now back to silent running.
A very good friend of mine services hundreds of computers every week. He tells me he *always* begins by vacuum cleaning the computers. It's amazing what rubbish those fans suck in, and I'm thinking the Surface Pro's fans can't have much clearance inside that narrow chassis, so getting any dust out is a good first step.
Start with the computer powered off. Attach a vacuum cleaner hose to one of the vents using Duct Tape, or similar, to get a really good seal. Power on the vacuum cleaner and rotate the Surface Pro in all directions. Give it a few slaps on the chassis (NOT the Screen) to help dislodge any trapped particles. If my friend is right - and he invariably is - you should get a lot of dust and detritus out. This will improve the cooling airflow, even if it doesn't immediately cure the problem. Repeat the process on both sides, as particles that are trapped sometimes only release when sucked in one direction.
DO NOT be tempted to use one of those Air Blower aerosols. They spray a liquid gas (usually Butane) which may come out partially in liquid form. This isn't something you want on a live circuit board. And, yes, that circuit board is still partially live after shutdown! That's part of the reason why the Surface Pro can start up so quickly.
Hopefully, this will work for your Surface Pro.
Good-luck, Rick