2000 Sonata Vibration from rear

I have 2000 Sonata has a vibration from the rear passenger side that started off as just annoying. I took it to the muffler shop to see if it was in exhaust system. I cleaned out my trunk to make sure it wasnt there anyway it has gotten much worse and now is vibrating whole car at times. It seems to go away when applying the brake and when cornering. Where should I look ??