When my furnace is in defrost mode (fan not turning outside) I hear a loud noise that sounds like there is something flapping underneath the house. I have been under the house and checked all the duct work and found nothing loose. 2 different companies have come out to check it and of course it...

Can I continue running my unit when it makes noise when it comes on, what would cause it to do that

When my air conditioner turns on inside my house, it makes a thumping noise. Sometimes you can faintly hear it continually until it kicks off. It may be worse one day and not so bad another. I need help please!

My c/a has been running fine, but it makes a few second grinding noise right before it comes on and right before it goes off. The unit itself is only 2 years old, but my furnace is pretty old. Is this something I should be concerned about.