Strange vibration while decelerating!!

Help needed please......
The issue is a follows:
when i am accelerating, there doesn't seem to be a problem, but when i back off of the accelerator, there is a shaking / slight knocking noise from the front end - mainly felt through the floor (i think it is coming from the passenger side)
after some advice i have done the following with no joy.
Had wheels balanced
rotated the wheels
and i was also told to change gear when the shaking was happening, so i did this, and i even knocked it into neutral, but both made no difference to the noise / vibration.
any help and advice appreciated.

Thanks,
Dean.

How is your alignment? That's next IMO