Noisy 300E Exhaust

I have a '91 300E with only 53K miles on it. The car is in perfect condition and has had frequent oil changes using Mobil 1 15W-50 and MB filters. It passed Arizonas emissions test last year with flying colors.

I recently had to replace the exhaust system because of a rusted weld. Everything back of the cat was replaced with genuine MB parts.

After the new exhaust was installed, the sound of the exhaust has been somewhat louder than it should be.

I've checked for leaks several times and haven't found any. My question is this...

When the new exhaust system was installed, the mechanic hammered on the tail pipe of the cat trying to get the resonator off. Could that have caused some internal damage to the cat which results in a noisier exhaust? The loud exhaust note seems to be coming out the tail pipe and not at some point in the exhaust system.

Thanks in advance.