When it is really cold latley, I have a noise like a little fan spinning at high rpm. Starts when I turn on the ignition, even before the car starts and goes away about 3 minute later. I took off the cover for the ECU and it sounded like it was right in there. Dealer couldn't hear it as it wasn't doing it when I stopped in. They though it might be a fan in the ECU but I don't think that there is one in the ECU. It's no big deal but I just wondered if anyone else has or had it. The regular heating fan still works fine so it isn't envoled.

 

The only thing similar I experienced was the blower motor for the HVAC. A couple blades somehow broke off and were rattling around inside the housing. The rattling has stopped, so I haven't bothered to get it fixed.

 

I have had a similar humming sound myself. It too is really noticeable when I first start the engine. It does seem to go away after a couple of minutes. It seems like when the engine get to its warmed up temp, the sound fades away. I don't know my friends, Its a mystery. Has anyone noticed anything funcky with the electrical system?

 

Could it be the air pump for the polution control system? It does function more frequently during the cold weather.

 

I've noticed a similar sound since day one ... almost like a subdued high pitched whistle/whine. I only hear it on a cold engine start and it quits shortly after the idle drops to its normal level. Infinity's answer sounds very plausible to me.

 

Well I don't think its the smog pump. I'll get under the car tomorrow and take a closer look.

 

The noise is just like a high speed fan but you do not have to start the engine to hear it. Just turn on the key and there it is. I know that it is either in the ECU box or something right under it and actually touching it as the sound is right there. I noticed that there is a control module box cooling fan and I'll bet that it is the culprit. I have to leave it at the dealership overnight so that they can hear it for themselves.

 

Just noticed that the Control Module Cooling fan is located inside the front lower section of the Control Module box. It is wired to the Body Control Module and is switched on when the ignition is turned on. AH HA!!! It is attached via a duct from the passenger compartment to draw air to cool the Powetrain Control Module box. I'm willing to bet that the sound is, that fan.

 

Confirmed that it is the CM cooling fan. I turned on the ignition and opened up the ECM box and right at the front you can see the 1 1/2 inch fan exhaust and it was blowing air. I wiggled the outlet and the sound changed. That's it! Now to get DC to hear it.

 

I think that is the same noise that you can find in the MB ML suv under the dash

 

its a unique feature to the MB 3.2 liter V6. This is a rapid heating of Catalytic Converter feature and it makes that humming hi rpm fan sound only on cold start ups to warm the cats quickly.

 

Bullfrog:
Haven't heard anything from the Cats yet but the noise I experienced is the cooling fan at the front of the control module box. It's happening more often and DC has one on order.

 

You misunderstood, the noise I'm talking about is the same one you're talking about coming from the front area like a fan real quick, this to my understanding is a feature of this engine and somehow that sound is something that is causing the cat's to warm up in under 1 minute due to the technology in this engine. I have attached a link of this information for your review. http://www.whnet.com/4x4/new_V6.html

 

Bullfrog: Nice engine pic! I understood what you meant but I found the noise in the fan for cooling the ECU. It is at the front of the ECU black box and when it is making the noise I can actually grab the active fan and the noise changes, so it is just the fan itself. Thanks for the input. I'll let you know for sure when DC does the job.