Growling sound at start-up
 

For the last few weeks every once and a while when starting my 2007 SL550 I hear a growling sound. It is very short lived and does not seem to impact the performance of the car. In fact if I shut the car off and re-start it the growling sound is gone. It seems to be random in nature. I can go for days with out hearing the sound, and when it happens it is only once. The sound seems to be coming from the left side of the engine. Any ideas of what to check or look for?

It may be the ABC pump. They an make a bit of noise on warm starts since the fluid is hot.

It also could be starter not disengaging.

I have attached two audio files that illustrate the question I have. Typically when the car is cold the start up sounds normal, once the car is warm from time to time I hear the growling sound when starting. The car seems to run just fine, I do not have any error codes nor have I seen any performance issues or changes to my mile per gallon. Is this something I should be worried about or not?

Don't see any attachments.

Fixed the upload issue. Thanks for pointing this out. :)

I'm having a hard time hearing anything specific, but that may be my bad hearing caused fro too many rock concerts and loud car stereos of my youth. Another noise I sometimes here on mine with a warm startup is a bit of growling from the BC pump. I think it has to do with the warm fluid being thinner. It's always done it, and I've heard it on other R230s so I don't worry about it.

Thanks Rodney, the sound is just a little more of a rumble when starting than I normally hear. It sounds like it is coming from the front left. Doesn't seem to affect the car so I will keep an eye on it and if it gets worse take to my trusty mechanic.