maybe record the noise and post a link to it? also in the US the driver side is always referred to as the left side. you say it is on the driver/right side so not clear what you mean.

 

Thanks for your reply. The noise is from the right bottom of the engine when you are sitting in the car. I am in Australia (steering wheel is on the right). I can understand my post was confusing. I have fixed it now.

The noise is like from a 0.5hp electric water pump or a small coffee bean grinder. When the noise starts it stays constant at same frequency for 15-20 mins. If I disconnect the battery and reconnect it, the noise starts again. I have to keep battery disconnected for 20-30mins before reconnecting for the sound to go away. I don't understand what part around engine block can use battery like this when the ignition is off. Initially I thought it was something trying to cool the engine but water pump, oil pump, alternator and most visible moving parts stop as soon as the engine is turned off. I checked the regulator fan and its not making this noise. I have no idea whats making this noise.

I will record the noise when I get home.

 

I would guess it's something to do with vacum or fuel pump/pressure. Once I started the car and backed out the garage into the driveway then turned it off. While washing the car I could hear a whistling noise in the front/Driver side. You had to be within 2 feet to hear the noise and it lasted about 15 - 20 minutes..

 

Thanks kalc240. The noise from my car is loud and can be heard from 8-10 feet. After reading your post I read about Fuel Pump Check Valve and Fuel Pumps (HERE). Maybe the pump is trying to build up pressure after I turn off the ignition and its unable to build any hence the noise. I will try to find ways to check the pump. Sometimes (once every two months) my car doesn't start for a few mins and then after a while it starts with lots of smoke. Recently it also started making a back pressure noise when I turn on and turn off it in 2-3 seconds. Maybe this is all because of the pump or valve. I will check and post results. Thanks for the tip.

 

hi
same problem as analyst
can i know what was the solution

 

Well it definitely sounds like some sort of a electrical pump.. I might be wrong, but I'm thinking there is a "heater" re-circulation pump on these cars.. The think it's somewhere on the right, up around the reservoir tank... it's just a thought..

 

If you have the "REST" function on the ACC panel, it can run the electric coolant pump and cabin ventilation fan, but you have to specifically press the button before exiting the car.

 

the electric coolant pump check engine temp when it stops running..

 

I'm a junior DIY'er here, but I'll give it a shot. Most of today's engines are built under vacuum, the only thing i can think of is a vacuum leak of some sort. If it still occurs while the engine turns off then dies over time, its some thing that's under high pressure. Air or coolant or refrigerant... It has to do with a small breach somewhere. If it creates a very high pitch sound, its a small hole, if its a deep throaty sound its a large hole...My guess is check anything vacuum related, air intake hoses, dip sticks, PCV and other type of coolant valves, A/C lines. Refrigerant is under high pressure...check to see if you are blowing cold cold air...but, if it only goes away by disconnecting battery only, its electrical...

2 cents

 

I have the same problem. Noise is coming from thing front centre of motor.sounds like electrical pump...

 

Not the electric pump.... it’s the radiator fan. It goes off after few minutes.... Nothing to worry about

 

Same problem here with my 2002 C240. Just happened today for the first time. I checked the coolent temperature and it was normal. The noise was deferentially from the right side, like the other people described. At first I thought is was my electric fan running like crazy, but I looked under the hood and it was not running at all. Starting the car and turning it off again several times did not make the noise stop, but it did change the sound a little during the start as the power was drawn to the starter as would be expected.

 

When you hear the noise, put your hand on the auxiliary coolant pump (green arrow) and see if it is running. You could also pull the electrical connector to see if the noise stops.

This is most likely the noise you here and not a cause for concern.

 

I’ll try that, thanks!

 

2002 e320 here makes nonstop chirping started when i opened the door this morning.. Low in pass front fender . just drove 20 miles .. No problems sound never changed .. Car on or off with or without batteryHasn't stopped for 7 hours... Even with battery disconnected

 

This is the alarm siren and a known issue with Mercedes of this age. The alarm siren has it's own rechargeable Ni-MH batteries to prevent someone from disabling the alarm system by disconnecting the main battery. Over time, they leak and corrode the circuit board leading to a non-stop alarm.

You have three options:

1. Replace the siren with a new one (about $130 +/-)
2. Take the old siren apart, hope the damage isn't too bad and replace the batteries (Here is a DIY from the SL forum. Same siren)
3. Remove the old siren and live without it.

Instructions attached. Good luck!

 

Update: I figured out what the sound was on my car. It was the air injection pump. It’s a smog thing to inject air into the exhaust. It smelled burnt. I replaced it easily, only took about five minutes. The check engine light is still on. I don’t know if I got a bad pump or if I need to replace the relay or fuse yet. I still need to work on it when I have time.