That is because P&W uses a 747 to test all their new turbofan engines. GE does the same with a 747 as well. I want to say even Rolls Royce even uses a 747 as their flying testbed. Granted, all 3 engine manufacturers made engines for the 747 anyway lol
Also, a random thing about the previously mentioned sound of the A-10... The TF34 turbofans it uses are nearly identical to the turbofans used in the Canadair/Bombardier CRJ-200, the CF34. The Lockheed S-3 Viking also used the same engines. Old ass engines too, as they use a throttle cable unlike the FADEC controlled throttle by wire that the Embraer ERJ-145's I work on have.
The ERJ-145 uses the Rolls-Royce Allison AE3007, which can also be found in the Cessna Citation X and Northrop Grumman RQ-4 Global Hawk UAV. The basic core of the engine is also used in the RR AE1107 in the Bell-Boeing V-22 Osprey and AE2100 in the Lockheed Martin C-130J Super Hercules and Lockheed/Alenia C-27J Spartan.
Anyway a random pic I took at work a few months back: