V90CC knocking noise passenger footwell area

[yanto]

My V90CC has for the past 8 months had an intermittent knocking noise, it varies in intensity from barely audible to loud, my Mrs has even said she can feel it through her feet/bum, the real problem is that it being intermittent the garage have not been able to find it because they haven't heard it, me saying what it is and where it's coming from has not brought much action from my local dealer.

The knock will start and be regular for a period of time, then often stopping after a particular big hit, as if something is coming loose then going back into place, it isn't suspension as the knock is a fraction after hitting a bump, it's also brought on by change in direction.

Has anybody else had this problem, and if so has it been cured and what was it?

PS still trying to locate the fuse box in the rear load area - that has me stumped.