This is for my 99 sl1. the noise seems to be coming from 2 places but it could be just 1. Its coming from the front most likely under the hood and either in the center or both the driver and passenger sides. If it is both sides it sounds a little louder on the passenger side. Its hard to pinpoint where the sound is coming from as Im listening from the drivers seat. I can't hear it at idle but it starts around 30mph and increases with speed. I think its the wind vibrating something. reving the engine has no effect on the sound. When I drive around a bend the sound almost completely stops...almost. It gets more quiet on a curve to the left than it does on one to the right. Motor mounts look ok and I can't see or feel anything else rattling around under the hood. Any suggestions?

 

Possibly a wheel bearing, tire balancing, or tire wear issue if it is sensitive to turning...most suspension noises in these cars are clunky....

Or maybe the hood itself? There are 2 rubber stops on the front of the chassis where the hood meets -- they are height adjustable. Though I would think that changing rpms while not moving would rattle the hood....plus this doesn't quite fit with the turning stuff unless the frame is flexing a bit

damn hard to diagnose over the net....

 

I doubt its the tire balance or wear, I just got new tires because they were getting bald and I thought that might be it. The sound was there before and after the tire change. How exactly do I check the wheel bearing? I didn't know the stops were adjustable. I'll give those a look. could it be those rubber grommets where the radiator attaches I think mine look funny but what do I know... If anyone has a picture of how those should look please post them so I can compare. If you (or anyone else) have any more ideas please share.

 

prob not radiator mounts -- indeed they look kinda funky --- just the way they are...

wheel bearings are easiest to check with the car off the ground (the entire front that is..) -- support your vehicle safely!! If the bearing is badly worn, you'll find play when you pull out firmly on the tire.

You can often hear the grinding/moaning of the bearings in the vicinity of the wheel hubs when you rotate the wheels-- some folks have been known to put the tip of a long screwdriver against them as an amplifier and listen to the other end....