30 yr old Jantrol 21 series Model 100, 90K BTU nat gas furnace. Constant pilot.single stage. NO a/c. A loud buzzing sound has developed. It starts upon a call for heat and stops shortly after the flames fire up. Lasts probably 2 minutes total. Every time there's a call for heat. Its pretty loud . Any ideas appreciated. Our yearly isn't until Feb and Im wondering if I can hold off until then or its something simple. There's not much to this furnace. Blower-Transf-Fan-Limit-Gas Valve.Thats it. Any ihelp appreciated.
Eric

It could be your low voltage transformer making the noise. The old style furnace you have is very simple in design with not to many parts. It could be the gas valve is old and drawing a bit more current taxing the low volt transformer. If it bothers you I would call a pro and get it fixed before the winter.

The 24vTrans is the Original Honeywell. Could I replace it with a new HW 24V trans? OR There's a 24V transformer(EWC) on my zone control. Could I replace it with one of there's? In other words, if it mounts up OK wpould any 24V trans do?thanks

It all depends upon the VA rate of the transformer. It is OK to replace one with a larger VA but you should not replace a transformer with a lower VA. NOTE VA is the Volt Amp rate for the transformer. Different items in different equipment require different capacities. Also check that the imput voltage is the same. 110/120 volts is common on that equipment.

I think Ill replace the transf and see what happens. Thanks a lot.

One more question. I just took a look. The noise stops 2 seconds after the blower kicks in. The trans is down low mounted on the blower motor. The noise doesn't come from the transformer itself. It comes from the upper compartment where the relay-limit-gas valve is located. Would the noise from a faulty transf come from the transformer? You mentioned the gas valve as maybe being the culprit. If No noise by the Blower and trans can I rule them out?

It could be the valve. Try to listen closely a few times to see.