Exhaust alignment would be my guess. Had the same issue with mine. Through areas at low speed going over minor undulations in the road is the time you will hear it and yet nothing at high speeds or anything above 20-30mph for that matter.
Sounds like its coming from under the handbrake maybe slightly to the rear passenger footwell.
Renault sorted it for me, was to do with the alignment of the centre section and backbox on the car in relation to the diffuser etc.
Its a wallowy hollow unexplainable one......