As a side effect of the grounded antennas I found out the reason of the weird element vibrations. During the maintenance work when I moved around the antennas accidentally I clashed my head into the low hanging element tips and the strange noise was audible again.
I use 10-15cm tubing overlaps for these elements with a single clamp at the mid section. So in case of any stronger wind the inner 10-15cm is long enough to resonate and touch the outer tube which made the vibration noise. I fixed these ends with pop rivets to prevent the tubes to touch each other again.