To me, the loudest part of most driers is the fan that blows across the hot coils. They use a Sterling cycle, basically, so there is what amounts to a condensing coil, not unlike the condenser on your home ac unit. When they cycle on, they are moving a lot of air. I've never worked with a small one, but the large ones are fairly loud. Not as loud as the compressor of course, but they do make some noise.
I thought they were required to publish the noise level on their equipment. They do on their compressors. Or at least the ones they think are quiet enough to brag on. They do have some pretty quiet ones. Ones that you can carry on a normal conversation while standing next to. If you can't find it, I might be able to make a call or two and get a number. I know some compressor people who used to work for IR.