On braking when regeneration is occuring we sometimes get a clunking noise. on 2011 Lexus RX450h

The noise is not predictable but occurs more on light braking. It sounds like a solenoid chattering from underneath the car. Could it be the ABS modulator? Last year the dealer bled the brakes and the noise disapeared for 6 months, but now the cold weather is here it has re-appeared. Some days it occurs a number of times and other days it doesn't occur at all. It seems to occur more during cold weather.

Asked by for the 2011 Lexus RX450h
should be underr factory warranty
It is under warranty but the fault has now occurred again 6months after they apparently fixed it by bleeding the brakes. I am worried that it will occur some time again in the future out of warranty.