A judge ruled yesterday that the lawsuit filed against Madonna and the co-op where her apartment resides will be allowed to move forward based on the evidence provided. Madonna and the building owners claim that Madonna never violated existing noise ordinances, but that may not be the deciding factor if terms of the various leases dictate otherwise.
While it may not be illegal for Madonna to make noise in her apartment during certain hours of the day, there may be a clause in the lease of her offended neighbor that entitles him or her to quiet enjoyment of their own premises. If said quiet enjoyment is infringed upon by Madonna's activities, then she has a valid complaint. Of course, the complaint may not ultimately be Madonna's to rectify - and it's likely that she will not face anything other than a potential order stating that she can't use her apartment as a studio - or placing restrictions on the noise level and hours of the day she might use the space as such.
Ultimately, it might be much easier for Madonna and her neighbor if the star decided to use one of the many studios in the area for her needs. Everyone loves to work from home - sometimes - but overall it can be a drag.