Rhythmic knocking: Very likely the exhaust moving around and making contact with something else under the car. Check your hangers and mounts.

I had a similar sound come from my 300D approximately halfway between my origin (Nevada) and destination (Georgia) on a cross country trip. I was a bit worried until I looked and realized I just needed some new muffler hangers.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.