Exhaust blowing- leakage?

[dangerousdferrari]

Hi all,

My '99 Boxster recently had its latest major service and the slight rattling of the exhaust was supposedly fixed by Porsche, at an insane cost for 6 new screws....
The problem came back after around 2 weeks, so it took it back to Porsche and they said the only definitive fix would be to remove the loose heatshield.
3 weeks later, after a problem free MOT and fuel service, the exhaust seems to be blowing a little upon start up. Then, when accelerating, it is making a 'clicking' noise that echoes terribly from any nearby walls or cars on the passenger side (RHD - UK model).
Can anyone tell me if this is leakage from the exhaust as I seem to gather from previous information posted on this forum? Which part of the exhaust could be causing the problem? And could it be Porsche's fault for removing the heatshield? Apologies for sounding naive, or dare is say dumb, but could the fuel service of increased efficiency so much as to have caused the problem?
Any help is much appreciated as I'm reluctant to revisit my local Porsche centre for diagnostics after them trying to fleece me for unnecessary work on my major service - work that incidentally deemed totally unnecessary by an independent dealer.

Thanks for any contribution.