Idles real high at stops and makes noises in the exhaust under car.

More information please. What year is this vehicle? Is this a constant high rev or is it surging high then low and back again? Are you sure it is oil from the exhaust? Using a pair of rubber gloves, rub some of this 'oil' between your finger tips, oil will feel greasy. Sometime soot can form in the exhaust, especially on diesels, and when this mixes with water it can look like oil.
This 'Air Noise'. Is it a whoosh, whistle. hiss? This information can give clues as to where the problem is. Air noises, over rev and oil from the exhaust could be more than one problem. Get a Good mechanic to look at this and to check the Turbo and all the pipes for issues.

I suggest you have your car checked as soon as possible - while a rattling exhaust isn't desperately urgent it could be the cat breaking up which might later restrict the flow of gases. Most importantly excessively loose timing belts or chains tend to make most noise when the engine is idling. If the noise is being caused by this delay could be very expensive.

Chances are that a heat shield located under your exhaust or the catalytic converter has broke loose and rattles when you are idling in drive. This is common on older cars and is only usually noticed while idling in drive because the engine is working under a slight load and runs a little rougher. A good exhaust shop could probably fix it for very little.

It's your exhaust mounts or broken exhaust bolts. It does it in drive st idle n under load because the motor is sitting in rubber mounts made to dampen vibration. Therefore the motor tilts to the left in reverse pulling the exhaust away from your under carraige, and to the right in drive causing the loose exhaust to vibrate against something. Check your heat shields also. They fall apart n do the same noise. Piece of cake.

Check to see if one of your brackets holding the exhaust pipe has come loose. That'll make a rattling sound - especially if it towards the end by the tailpipe. When you're accelerating - more air is forced thru your exhaust at a faster rate, so it's not moving as much as when you're sitting still and the truck is just at an idle with less air/exhaust moving thru the tailpipe. If it's only making the noise while the truck is stationary & the noise stops one the truck is moving - that pretty much rules out anything to do withe the drive-train or suspension. You are sure the noise is from the back & not coming from under the hood? If under the hood - check your oil level ASAP.

It is most likely an exhaust heat shield or a catalytic converter that is breaing apart inside. Get underthe van when it has cooled off and "thump" the exhaust with your fist to see if you can locate the rattle. Often, the heat shield welds break where they are attached to the catalytic converter. I have fixed many of them by taking 2 or 3 large screw-type hose clamps and screwing them together to make them long enough to reach all the way around the catalytic converter and tighten them down to stop the rattle. If the noise sounds like it is coming from INSIDE the converter, you will have to replace the catalyst. (or ignore the noise)

Could be something jumping around in the exhaust. Is your catalytic conv in that area?

sounds like it is most likely an exhaust heat shield. they make alot of noise and the simple soution is to get under the car and hit them to see which is the culpret and then rip it off

Check the exhaust compression. Remove the O2 sensors before the cataylic converts and see if it improves. If it does that means your cats are cloged and need to be replaced.

This seems to be a classic case of "disentegrating exhaust system syndrome." There is either a hole(s) somewhere in your exhaust system or there is a leak somewhere. Probably the easiest way to tell where the noise is coming from is to start your car and just listen around in the engine bay, under the car, and at the muffler. Also do a visual inspection of the exhaust system to see if you can see any holes in the piping. I have also seen hairline cracks in the exhaust header itself that can cause the loud ticking noise that can be a little tricky to track down.