Hi my girlfreind lives in a mobile home,with original heat and air. I believe its around 1985. She describes a noises coming from blower but stops if you hit. I don't know if it does it any more after that. I think it comes and goes so she keeps hitting it.anybody have some ideas. Any ideas would help. Thanks

Motor mounts for the blower motor.

Loose or dirty blower fan blades/squirrel cage causing out of balance condition.

Probably needs a good cleaning and service. Most of these units are neglected.