Smoke coming out of heater

[George D]

Gas heater has not been used for over 5 years. When turned on, it works but after about 10 minutes, smoke comes out of the top of the heater, near the pipe.
Is this normal for a heater that hasn't been used for a long time?

 

[Brianf60]

Try cleaning it out. Use compressed air or the outlet of a vacuum. Blow the dust and debris out..

 

[George D]

Will try tomorrow morning. Thanks.

 

[George D]

The smoke is gone and the heater is working. The only issue is it's making a continuous clicking sound, like popcorn popping.
Is this a problem?

 

[JamesW]

Might be water boiling. Need to have it checked. Leave it off until you can get it checked.

 

[George D]

Thanks, I'll get it checked. While it was working the heater made the garage hot. Can this be from blockage due to debris?
Also, there were bubbles coming out of the returns when it was on. No bubbles after I turned it off.