Choosing mufflers

I am running 360 engine w/340 HP manifolds in 21/2 pipe back to Magnaflow mufflers with tti X pipe connecting. 21/2 back over the axle to 340 SS tips. Problem is at 1900-2000 rpm down the road makes a drone that don`t go away until at least 2500 rpm. Running 3.55 gears with 14 in tires. I was running standard dual exaust to sunnit turbo mufflers- couldn`t stand the drone went to magmaflow, I think their are 20 in case and it has a really bad drone. also running a A500 tranny. Need some help very badly. Thanks