Flowmaster drone solved.

So I installed a 2.5 inch dual exhaust using Flowmaster mufflers on my car about 10 years ago and always hated the sound and especially the wicked drone at cruising speeds. At the time I didn't do my homework (should have went with Dynomax for sound and flow) but I have been living with it. I didn't really want to remove the FM's because they are in great shape and welded in the system. I decided to try an H-pipe and WOW did it make a huge difference. I have yet to put the tips on but it sounds more crisp, raspy and deep with no more drone.
I wish I had done this years ago!! The H-pipe kit was cheap and I upgraded to band style clamps. If it matters I am running a mildly cammed LA 360 with hi-po 340 manifolds. I believe the mufflers are FM 40's.

Hope this helps.