I've got what sounds like a rattle under the hood when I accelerate. Once I'm up to speed it goes away. Have been running Shell 89 octane lately.

Some history:
The combustion chambers do have some amount of carbon in them, visible through the spark plug hole. When I first bought the car I did a compression test with readings in the 180's, all cylinders were within range of each other...

Recently did the water + Sea Foam injection through the intake manifold and my compression readings went down to 150,170,150,150 (same guage was used). In addition, just like in one of the other threads below, my engine wobbles at idle. (I plan on following some of the recommendations from that thread to hopefully cure the wobble)

So what could be causing the rattling under load?

Thanks,
Zuda