1) Squeaks
Be sure to check all the plastic body panels, in particular the rear wheel fairings, to make sure they are securely fastened. Nothing unnerves you more than hearing a funny sound, pulling over and finding one of your wheel panels partly slid down with a missing screw. (Keep trash bag twist ties for emergencies like this... an "ok" substitute until you can buy the $12 bolt.
Other than that, it could be ordinary car suspension sounds... you might be able to test this by standing above each wheel and firmly depressing the suspension a couple times and listen.
I've also had another car (not an Insight) that had some exhaust heat shield that kept rubbing on the exhaust in certain cases.
2) Gas octane
Low octane burns hotter... yes its true! The higher number is marketed like Ghz on a cordless telephone. (Didya see they now have 6.0 Ghz phones? People think its "better" the higher the #, LOL)
I live in Utah, and they have 85 octane there because of the higher altitude. The air is thinner and needs a hotter fire to burn correctly... so running 85 is equivilent to 87 at the lower altitudes. The reason to put in high octane fuel, is to have a cooler fire for
high compression racing engines to cut down on detonation/pinging. When I had my Mercedes C230 sport coupe with its supercharged engine, I had to use 92+ octane or risk engine damage. Now I use 85 when in Utah, and switch to 87 when forced to when I drive out of the area.
The insight has anti-knock control that makes use of the electric motor, you can use any grade of gas and it will run fine. I've heard tell that 92 octane will theoretically get you a tad more gas mileage, but you'll pay for it with the higher price of the gas, making it at best an even trade.
Use whatever is cheapest grade gas, at a top tier gas station. (
http://www.toptiergas.com), and your car will run just fine.
3) I haven't needed to do anything about clearance, but there were some threads on this forum about using Daewoo springs as a direct fit replacement.
-Shawn