There is a metal panel in the ceiling of the bathroom above the shower that when you turn the heat on it sounds like the sucking is coming through there. But there is an air intake where a filter goes in the hallway, but there is a dusty air duct running above that. So where is the air coming from since the noise is coming from the closed off space in bathroom?

Your post is a bit difficult to understand. You posted "intake". With a central system, there are heated air supply ducts with grills or diffusers and cold air return ducts with grills. It sounds like you have a central return ("intake"?) in the hall. "So where is the air coming from since the noise is coming from the closed off space in bathroom?" Air coming from what-? you said "sucking". You can use thin strips of toilet tissue to determine if air is being supplied or removed. I have never seen a cold air return over a shower but we have no idea as to how you system was installed. Typically, over the shower would be an exhaust vent to clear out the humid air. It should vent outside but in older homes it will vent into the attic. If you close off rooms, negative pressures can cause backflow, perhaps this is what is happening. Maybe redefine your terms and possibly a picture so we have a better understanding of what you actually have.

I am just trying to find the air return for the heat. I have pics, but it will not let me post it in this forum. Can I email to show?

Basically, where the filter goes in the hallway is a hole in the ceiling that contains just an air duct. The sound I was referring to was when the heat kicks on, you can hear it coming from inside the closed panel in the bathroom which I believe contains the furnace in the attic. I am just not sure where the air return would be?

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My guess would be "where the filter goes in the hallway". Filters are in returns. That duct should be attached to the return side of the air handler. Have you ever looked at the heating unit? "inside the closed panel in the bathroom which I believe contains the furnace in the attic". Can you explain that a little better, I'm lost.