Wow. back from the dead and got Sh**y quickly.

The 87s had an issue with the heat exchangers rattling and was supposedly fixed with an additional brace in 88.

Personally, I have only noticed this while starting from a stop, once moving the rattle went away. If it's getting worse at speed, you have different issue. There was a shaft update, but that should only effect clutch weight / shifting.

As far as 915 vs. G50, in a stock car it's moot. I prefer the 915 and found the G50 in the 80s Carrera to be dead feeling and sloppy... maybe I just had a bad one. My 993s were MUCH better.