W219 CLS parking sensor: beeping tone vs solid tone?

[philnewmerc]

Hello again. Anyone shed light on this? Had some parking sensors replaced. The front right sensor has a solid tone but the left one is a beeping tone... why on earth would that be?? Also, one at the rear corner still doesn't work but the system as a whole still seems to work... i thought one sensor not working normally stops the whole lot??? (That's why it went in for repair)

 

[philnewmerc]

Bump: just wondering why one sensor only beeps a solid beep at the end of it's travel but the other side has a beep beep beep noise... odd? Is that because I've got a different part number perhaps?