Ever fired a Pentax 6x7, Clarion? I tried one once, and leapt about a foot in the air in shock at the sharp "clop crack clop" it made as the mirror went up, the massive focal plane shutter went, and the mirror flopped back. No stealth photography with one of those, but its big enough to blot out the light from the sun, anyway. I'm can't recall who it was here, maybe you, who nearly got me buying esoteric 6x7 things...
I had an OM40, yes, it did make quite a sharp noise, didn't it? I later had a cheapie OM10 (divorce led to selling the OM40 and the Mamiya TLRs) which brought on the hunger, so I bought a S/H OM4... still miss it, after I sold it due to another financially tricky patch.
Getting wistful about 5x4 field cameras again...