electric heater noises

[Da_Pearces]

I was awakened this morning by a banging noise in my house. I soon discovered that it was coming from my a/c-heater closet. My heater was turned on and knocking noises were coming from the unit inside the closet. I looked at the thermostat and the light for aux. heat was blinking on and off, in synch with the knocking, as if it couldn't decide if it wanted to be on or off. I turned down the temp so the fan would go off and that stopped the knocking. But, when the temp in the house dropped and the fan came back on, the knocking came back.
I left the heater off for about an hour and just turned it back on becuase it is getting cold, so far so good, but I expect the knocking to come back.
Any suggestions as to what this might be?

[mattison]

Does it do this if you turn the heat off and put the blower switch in the on position. Just turning on the fan.

[Da_Pearces]

I had to turn the entire thing off the last time to stop the knocking.
I have had the heater on for about 30 minutes so far and no noise as of yet.

[Ed Imeduc]

Id still turn power off and go into the blower part there. See if the blower wheel will move up and down and in and out some . Wheel loose, motor bearings bad something in the blower. Is filter clean, coil clean. Aux on, was it in defrost here? When its knocking Is big copper line hot or cold?

ED ;)