We just bought a 2004 Neon RT from a private party. It has 98k on it. The owner said that it has a stage 1 chip.

It sounds as if it has an exhaust leak somewhere between the header and the cat because in 1st, 2nd, 3rd there is a loud vibration. The owner said it was a motor mount, but looking at the mounts, they all look ok and it doesnt feel like a broken mount. What might it be? In 4th and 5th gear it seems to be quietier or not there and its only there when in gear (if I clutch in, the noise stops). I havent gotten under the car yet, but what else could cause it?

The car has 17" wheels from the SRT with low profile tires. The car has been lowered but I cant tell how much. I'm assuming 2" - 2 1/4". It actually feels like they cut the springs instead of installing proper springs. I want to raise the car a bit with better springs, maybe a 1 3/4" or 1 1/2" drop instead so I can get some bigger tires, maybe some 16" wheels instead. What is a good set of springs and struts to go with them? I've used eibach springs with tokico struts in my camaro and was very happy.

Also, with the stage 1, can I safely run 87 octane? The owner said to only use 91 but that is crazy. I have 89 in it now and it runs fine other than the vibrations.