Unexplained noise

[Tolley]

Noise believed to be coming from rear of car. Sounds like an 'acoustic ping' (think of WW2 film where ship is looking for submarines). Far quieter than the noise you get when a door is left open. Was at the same regularity regardless of the speed of car, & it continued even when the engine shut down whilst waiting at light/junctions. As an abstract I thought it could be something to do with fuel pump, but that doesn't seem to make sense as it continued when I parked with engine off. Came back to the car a few hours later & the problem wasn't evident on the way home. Friends were in car with me and we all heard it so I am not crazy). Car is a 2017 C200.
Anyone had this before?

 

[whitenemesis]

Seat belt warning? One of your passengers not wearing the belt?

 

[Deletedmember130310]

Anything heavy on any of the seats?

 

[liamt]

Definitely sounds like the seatbelt warning for the rear seats. I believe if you have the radio on it also temporarily dips the volume so you can hear it. Had this a few weeks ago when a friend forgot to put his belt on. The seat belt sign should also reappear on the instrument cluster.

 

[Tolley]

I appreciate each of your responses, thank you. Have just been out for a v.quick spin to test the theory(s). It was just myself and my wife in the car. Whilst I had the ping when she was occupying the front seat without a seatbelt we didn't get any audible warning when she was in the back without a seatbelt (is that correct?). That also doesn't explain why it was still pinging yesterday after I had parked up and was walking away from the car... I am going to pay attention to it over the next few days and see if I can get any more clues.
Thanks again.

 

[Tolley]

Greenmansslk - interested to understand more about 'anything heavy on any of the seats'. The front seat passenger was stout! He also sat in the same seat on the return jpurney when we didn't get the pinging..
Cheers.

 

[Deletedmember130310]

Greenmansslk - interested to understand more about 'anything heavy on any of the seats'. The front seat passenger was stout! He also sat in the same seat on the return jpurney when we didn't get the pinging..
Cheers.

I was referring to the earlier comment about the seat belt warning - i have had it trigger with a heavyish bag on the seat, which fooled the sensor into thinking the seat was occupied

 

[PobodY]

Odd SRS warning can manifest like this. - Our CLK sometime suffers from a seatbelt warning error from a loose connection under the passenger seat; as it comes and goes it took forever for us to catch the warning message and solve the problem.

Obviously that's only something that makes noise when the car is in motion.

 

[Tolley]

Ok, got it. Thanks...

I was referring to the earlier comment about the seat belt warning - i have had it trigger with a heavyish bag on the seat, which fooled the sensor into thinking the seat was occupied

 

[Tolley]

Odd SRS warning can manifest like this. - Our CLK sometime suffers from a seatbelt warning error from a loose connection under the passenger seat; as it comes and goes it took forever for us to catch the warning message and solve the problem.

Obviously that's only something that makes noise when the car is in motion.

Not sure thi sis the same problem but thanks any way.

 

[Dodipops]

Does it have a towbar?

Maybe got a bypass relay fitted and it’s chirping away to itself in the boot somewhere.

 

[Tolley]

No tow bar fitted, however the relay is an interesting thought. I didn't hear it yesterday albeit I will keep listening.Thanks Dodipops.