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
RepairPal Certified shops can diagnose and repair your 2002 Mercury Grand Marquis. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
