My Goodman furnace has intermittently started to make a chattering noise just before it goes on. Not all the time buit it's starting to make the noise more frequently just when the furnace starts. Once it starts it's quite and working fine. Sounds almost like a bad selinoid in a car. A short chattering noise then it either stops and the furnace works OK or it stops and nothing happens until it tries to start again. Then sometimes it's just fine. Any ideas what's causing that. Once it goes on it woreks fine.

I would check all grounds to the unit and to the controls in the unit. Chattering is usually caused by a low voltage condition.