Lots of questions about 97 Eclipse

I drive a '97 Eclipse GS, automatic, FWD, 2.0 liter, no turbo, 99k miles

I've noticed when I start up the car, the engine idles at about 1,500 for 1/2 a minute, then drops to 1,000 slowly. After it hits 1000, it will start to idle roughly, then drop to 900 or 800 then pick back up to 1000 then drop again and it repeats this cycle. Also tonight when I started it, I heard a high pitched noise, I couldn't tell where though. Further more, I hear a sound like rushing water when I start the car and it lasts until the car is warmed up and I've gone more than a 1/4 of a mile.

Any ideas about what that is or if I should be worried?

I've also noticed that when I'm driving at any speed about 35 mph, and I let the car coast, I hear a thumping or knocking noise coming from the front of the passenger's side of the car. It developed about 2 weeks ago when I was driving on the thruway in wet weather. I was doing about 70, and as I was increasing in speed, the car shifted but it lurched hard when it shifted and ever since then I've been hearing the knocking noise. I'm not sure if this is related, but the car has seemed to always shift much harder than any of the other cars I've ever driven (2004 Acura MDX, 2002 Nissan Frontier, and a 1990 BMW 325i)

I know the sounds are relatively recent because I just got a new radio about 3 months ago, and before that I went 6 months without any radio in the car.

Also, the car currently has 17" wheels on it, and the steering wheel squeeks when I turn it. The sound comes from the steering wheel and not the tire areas themselves, do the tires have anything to do with it or is it just standard noise?

Lastly, we bought the car used and it came with a single exhaust, but with 2 seperate pipes (I guess you could call them that) coming out of it. I was just curious if this was stock. Give me about a week and I'll post some pictures of both the rear of the car, and the engine bay because I'm not entirely sure about anything on the car since we didn't get an owners manual with it.

Thanks in advance for the help.

~Bryan

maybe your air filter or fuel flter , or somting else

for the idle problem and the sound of rushing water.....you might have a vacuum leak somewhere. check all the vacuum hoses for leaks. for the thunking noise. check out your suspension and stuff like that to make sure nothing is lose or wore out and check the axles too. your cv shaft might be on the way out. it might also be a good time for a transmission flush and a new filter. have your local service center do that for you.

as for your exhaust pipe question. The stock GS' stock exhaust only has 1 pipe coming out of the muffler. So if you have 2, then that means you either don't not have a stock muffler or the previous onwer put a tip onto the buffler.

check the coolant. start her up cold with the radiator cap off and have someone top it off from the cap. do so until all the air bubbles are out.