Testing 40D, 5D, and 7DII with noise meter app on my smartphone, at a distance of 10' all three fell in the 40-42dB range of noise (1/500 f/2.8), although all three were very different in the type of noise emitted!
The 7DII measured 40dB, the 5D and 40D measured 42dB, with same lens mounted on all cameras. A normal speaking voice measures about 50dB.
Most of the noise is mirror slap...if one slows down shutter to 1/8, and uses mirror lockup, the peaks are at mirror lockup and when (after shutter is released) when mirror drops...one cannot see a significant waveform change when shutter itself opens first curtain or closes second curtain.
This is the 40D sound, with mirror up slap at 42dB...(the 43dB shown is the noise of me touching the phone to pause the graph)