In the good old days, we used to take a drill to the silencers and put holes in them. It worked.
When I was a kid, I saved up all my pocket money and bought a Lotus with dual tailpipes. I thought it sounded glorious, until it was pointed out that both rear pipes were as rotten as a pear and it was blowing (a lot).
I had to spend the rest of my pocket money on a new exhaust....it sounded s**t afterwards. :roll:
On topic...have you done the 'golf tee mod' so the mechanical valve stays open all the time? :?
Takes about 20 seconds, if you look under the car just behind the exhaust tips you will see a small vacuum hose connected, if you disconnect it and then bung the end (I would suggest something more than a golf tee, I ended up using a bolt and clamp, but you must bung it and it be air-tight) to put it simply it will mean the exhaust flap is open all the time and not just when you boot it and the engine is up to temp.
Did it on my 28i when I had it, improved the sound in the cabin, and if you end up not liking it you just have to reattach the hose the to valve to undo it.