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2001 SLK 320
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Recently purchased a 2001 SLK320 with 6 sp manual and 82k miles. Needed some maintenance and TLC work which I have done. She drives great, shifts smooth, the check engine light is off and there are no codes pending. But there are two things I’d like to work on. First is an annoying noise that I believe is coming from the rear (setting myself up for some jokes there) that:

- only occurs during light to moderate acceleration in virtually all gears from 1500 to 3000 rpm (most prevalent when in 4th at about 2100 rpm),.
- noise volume is soft at first, then gets louder as rpm’s get faster, then volume gets softer as rpm’s pass 2500/3000
- does not occur during hard acceleration or deceleration (with the clutch engaged or disengaged) at all, even through the rpm range listed
- when the car is making the noise, the noise will stop immediately after taking foot off the gas and start back up when gas pedal is depressed
- does not occur when out of gear, revving the engine and holding at 2000/2200 rpm (whether stationary or rolling)

The sound the noise makes is difficult to describe. It’s like a reverberating whooing/humm. At first I thought bearings, or differential, then maybe the fuel pump, or fuel filter….. I have not done anything yet to get rid of the noise. What can I check to narrow things down and eliminate this noise?

The second issue is when refueling, the gas pump automatically shuts off after a second of pumping. I have read other threads on this, but my CEL is not on and the car idles fine. Could it still be the Evap charcoal cannister? I’ve tried twisting the nozzle, pulling it out a little, starting with a slow flow then speed it up – but unless the flow is at what seems to be a trickle, the pump automatically shuts off. I tried different gas stations as well with no luck.

Any help with either of these issues will be greatly appreciated. Thanks.
 

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My 2001 SLK320 (6-speed, 100K miles) has had that exact refueling problem since it was new. Dealer has never been able to fix it, but I have an odd work-around... just be careful when you try this. This sounds sketchy, but it has worked for 10 years now... take a coat hanger and unbend it so that it is straight and about 25" long. Cut off any twists at the end, so that you have a nice straight wire. Carefully put it down the fuel filling tube, but be sure to leave enough so that you can pull it out. You'll need to hold the little flap open to extract it. You might need to twist the wire while inserting, and especially while extracting.

And that is it... like magic you can now fill your tank without problems, and the issue will likely not come back for another 6-8 months. I keep the coat hanger in the trunk along with the spare tire for this exact problem, and this fix works every time. Kinda annoying on a $50K car, but it works. Hopefully your dealer will have a better solution. Mine didn't.

Can't help with the engine noise I'm afraid... haven't encountered that before. My 2-cents guess would be an exhaust leak.
 

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2001 SLK 320(222K Miles), 2002 E320 Special Edition(186K Miles)
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Diff noise doesn't change with engine RPM, more related to speed or acceleration and deceleration.
On the 320 engines, don't ignore the possibility that the noise may be from the catalytic converters. They make a rattling sound at certain RPMs when the core starts breaking loose. Try hitting the cats with your hand or a rubber mallet to listen for any noise.
 
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