When does the noise happen?
What has changed(i.e. suspension work) and when did you first notice the noise?
You said you checked the exhaust, how exactly? Could the pipes be contacting the axle?
I see you have 55D springs which means the rear shocks were unbolted for their installation, have you checked those?
I also see you have a convertible which has additional structure braces, were those worked on or possibly contacted by the axle when doing the suspension work?
Also note, in case you did the suspension changes a while ago that does not mean they aren't to blame. If a bolt was snugged but not torqued it can still come loose.