I bought a pair of Ebay as well for my passengers. Used them for the 1st time at the weekend and they where dreadful! The amount of static feedback was appalling.
In the end I had to unplug the Microphone part of the headphone to get rid of the noise!
It seemed that everytime my passenger turn his head to look out the window the noise started. I have a feeling it is an over sensitive microphone in the headset with no noise cancelling! Unfortunately the Sqwelch didn't work either, so am going to see if there is something else that can be done!
I did only pay £40 for them so I wasn't really expecting them to be that great!