There was a turboprop airplane in the 1950s, the XF-84H Thunderscreech, that could reach Mach 0.9 with a prop. It was also so loud that the ground crew were injured by the noise alone and they eventually were required to tow it to the middle of the desert to take off. In the end even the test pilots refused to fly it. It remains the fastest prop plane in history.

I know the one you're talking about --- the ground crews nicknamed it "The Mighty Earbanger".

The problem with the XF-84H was twofold;

1- It used a propeller of unique geometry, which could not produce enough power to so much as taxi, without producing enough decibels to cause injuries to anyone in nearby (within 5 miles).

2- It was powered by a turboprop engine, which is the loudest type of aircraft engine yet conceived --- the turboprop-powered Tu-95 has proven near-deafening to US fighter pilots (behind tremendous noise-deadening insulation), and can be detected by NATO subs from hundreds of miles away (via sonar).

This resonance was a product of this unique combination of an overly-loud engine, and a propeller so small that it must produce tremendous RPMs just to move the aircraft. Both the engine and propeller were both poor, thoughtless ideas by themselves, but you have to wonder if someone wasn't deliberately creating a failure, in order to discredit the potential of propellers as supersonic propulsion mechanisms --- perhaps someone in the jet engine lobby had infiltrated the project...

The G-1010 Silver Sword uses a more conventional powerpack that would not produce any dangerous resonance, and would not be loud or impotent at low RPMs. The downside is that the engine and propeller alike would need to be overwhelmingly strong to withstand the forces that they would experience, and this would not be cheap --- hence, the estimated $100000 price tag (in 1942, a state-of-the-art warplane like the P-47 would cost some $25000, so if you adjust for inflation the G-1010 costs the equivalent of $100 Million , in today's US$).

There are C-130Hs flying out of Standiford Field (Louisville International Airport) and they are some of the most recent designs of turboprops (the 123rd Airlift got the 2,000th C-130 off the assembly line) and they seem quieter than the various heavy jets that fly out of there. (I worked at the main UPS air hub and it was funny to hear every car alarm in the lot right at the end of the runway go off after a 747 passed over on takeoff.)

Ooooh, I want one. Never played it, but a supersonic propjob, is my kinda concept.