I suggest you delete the ManiacBug version of the RF24 library and use the newer TMRh20 version which solves some problems. There is a link to it in my Tutorial.
Your TX program makes no attempt to determine if the wireless message has been received. To my mind it should only start the ultrasound when it receives an acknowledgement from the RX. Without something like that how can the two systems know that the noise corresponds to a particular wireless signal?
And you have not described what is different about the non-working version of the Rx program.
...R