I just put 4 new tires on my 94 g. marquis but it sounds like a scalloped tire, kind of like a flopping noise, we checked all 4 new tires and it’s not them. It faster when your faster and slow when you drive slower. could it be rear end, drive shaft, bearing’s or??
Could be a tire with an internal fault. This can be found by having a “road force balancing” done on the wheels. That spins the tire on a machine that presses a spinning drum against the tread to simulate road force, and it can detect internal tire faults that a regular spin balance cannot.