this might sound stupid, but are boxster exhaust systems rigidly mounted

[particlewave]

The engine and trans are mounted on flexible rubber mounts (same as any car). The exhaust is mounted to the the engine and transmission, not the chassis or body. The engine/trans/exhaust all move together.

Droning is caused by lack of cross pipe between the two engine exhaust banks. Stock mufflers and some aftermarket have cross pipes or phase chambers where exhaust gasses from the two banks are mixed so that the opposing sound waves phase each other out and prevent droning.