Traffic whistling

[Zagato]

Whenever I drive for a long time, or get caught in traffic, a weird high humming or whistling comes out from the right side of the vehicle. It clearly sounds as though it's coming from inside the car, and I have a suspicion that it's coming out of the right side air vent. The sound is mostly heard when stationary.

Any ideas what this is? I almost thought my car was overheating when I heard it the first time.

[BAR]

This humming sound may also be the fuel pump, the W116 uses an elctric fuel pump and when hot or worn can often 'whistle or whine'.

[Zagato]

This humming sound may also be the fuel pump, the W116 uses an elctric fuel pump and when hot or worn can often 'whistle or whine'.

Does this mean I should replace it as soon as possible?

[Hemersam]

I was interested in this thread about a "humming" sound when the engine is warmed up.  My experience is when I start my 280SE up in the morning (engine cold), there is a definite humming noise in the passenger area (can't tell where it's coming from); despite this, the engine seems to run normaly.  The humming sound seems to disappear when the engine warms up.  What could be the reason for this?   
Hemmersam

[John Hubertz]

I'd bet emissions - I'm not familiar - but some of the components bleed off air or bleed in vacuum - PCV valve systems can make some interesting noises if a flute hole appears in the popoff.

Air pump?  (don't know if Canada cars have one) coud be the sound as air is pumped into the exhaust due to a leak)

Exhaust donuts - these can have leakage that only occurs when cold - what would do it when hot I'm not certain

Lastly - the darned HVAC system controller under the hood

Just some ideas

[pez]

Max has some good ideas to check, but I would 1st check that fuel pump. Also, check to see if the sound changes with the volume and temperature of fuel in the tank. If more fuel or colder [freshly pumped] fuel minimized the problem, then the fault most likely lies with the fuel pump. Be sure to change the filter when you do the job. And also be sure to get the little extension piece that you may or may not need....trust me on this, as even the factory supplied filter as been super-ceded to the slightly shorter style which requires the spacer.