i have a de-cat and non res center section. basically straight through to a very minimal baffled back box. it burbles on overrun and has a nice humm on tick over. when you get it in the cruising zone its quite civilised but when accelerating its quite loud and if you give it some stick it sounds mental. tunnel runs never get boring

also i find that because there is nowhere for fuel to gather in a silencer in the center i get the odd pop and bang.
i only have a 3" downpipe reducing down to a 2.5" system but ill be doing the rest in 3" which will increase the bass in the exhaust a little.