Furnace will ignite +++ flame on for 5 to 10 seconds then somewhat a loud noise trying to switch on ++++ then flame shuts off ++++ 4 to 6 second delay then flame reignites +++ on for approx.5 sec. fans already on ++++ gas is on +++ flame does kick on every time+++

Appears to me the turn unit on switch not working??

What brand of furnace?
What model number of furnace?
Have you done anything lately to the furnace like new thermostat?