My car was like that too. It had some small Flowmaster mufflers on it that the drone was just too much... especially with the top down.It sounds great at idle but the drone at 45 mph is obnoxious.
I bought some cheap, short glass pack mufflers from Summit and installed them like the factory resonators in the tailpipes. The drone was gone! The car still had a nice sound at idle and I was happy with the results.
I drove it for a year and a half like that. The rest of the system needed addressing by then, and I decided to replace the whole deal with a TTI exhaust. If I had not done that, I would have kept the glass packs.