Can anyone suggest what's the possible problem with the furnace - it makes a loud clanging noise when the heat first come on and stop right after that.

I would say that your Blower wheel is broken or it has come loose on the motor shaft. Or one of the motor supports has broken.

More that likely it is the wheel loose on the motor shaft.

I would say that your Blower wheel is broken or it has come loose on the motor shaft. Or one of the motor supports has broken.

More that likely it is the wheel loose on the motor shaft.

Do I need a heating guy to fix it or it's something easy to fix?

Do I need a heating guy to fix it or it's something easy to fix?

That all depends upon your mechanical ability. If you feel you can find the problem,take it apart,find the replacement parts for the defective parts and reassemble then go for it but if you cannot do those items then call for local on site help.