2003 hums

My Impala hums while going down the hiway. It usually starts at 20 mph and quits when i make a left turn. I replaced the front rotors and brake pads last year and this started shortely after. The instrument panal gauges also quit working about the same time. The air bag light is lit, the brake light is on, and the abs light is also on. I have had it hooked to a diagnostic computer and was told that nothing is wrong. Any help would be appreciated.

Welcome to AF. The hum is a bad tire or wheel bearing usually, the abs needs to be scanned with a scanner capable of picking up abs codes, same for the air bag system, normal scanner will not work here. You need a better repair shop here.