Car making a hunming noise at about 20 mph and stops at about30 or 40mph...help?

Air suspension compressor components will make intermittent buzzing noise, but sounds like your concern is mostly speed dependent and not so much about the compressor if equipped. Hearing the noise would be quite helpful. Anyone near you that you trust to have a listen and give advice? Perhaps try one of the RepairPal Certified shops near you: Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops