I have a Q300 and SOMETIMES it does clang/vibrate against something down there. I've purchased KB XL hangers but haven't gotten around to installing them yet. But the noise does come and go.
Be sure of where it is vibrating/rattling/clanging.
If it's from the rear, then probably the muffler or some pipe.
If it's from the middle, then it's the resonator vibrating against a heatshield/floorpan.
Mine did this, and I just had to adjust the bolts on the flange between the downpipe and midpipe. All it needed was a small move to the left to center the midpipe.
No cost.