More sidewall on a smaller wheel can often make the ride less harsh.
Lift a wheel and tap on suspension parts with a mallet. See what talks. Anything obviously loose?
Trailing arm/Track arm is one of the most common rattles.
[Google/Bing/DuckDuckGo] site:986forum.com track arm rattle
Another common suspension rattle is worn out sway bar links.
Other than suspension, the heat shield on the exhaust coming loose can make a similar annoying rattle.