verified noise free in many installations. I have 2 on my RV and 4 on my Moose with zero issues.
In general it is a advisable to have a central ground point and not use the airframe for the ground path. This can be a source of frustration down the road and can cause corrosion issues for certain materials. Aside from that, it would be a good idea to check your connections for the jacks and other audio related items.