vibration with Janitrol gmn-80-4 (90 fcu) furnace

[budzzz]

After the blower is on for a few minutes there is a vibration type noise that lasts for approx 20 seconds then goes away. They had thought it was the new type of filter (pleated-90 day) they were using & decided to change back to they original type (fiberglass). The noise stopped for a while with the original type filter but then came back.

[htg guy]

Maybe a piece of the cardboard filter frame is caught in the blower wheel.

[drumn91]

What is the exact model number??
Could be the induced draft blower, maybe even a heat exchanger not installed properly at the factory via loose vestplate screws, crimping,etc. I've had some blower wheels out of balance due to the wheel weights moving on wheel vanes due to shipping transfer on trucks and thus throwing off the balance.

[HVAC Pro]

Sounds like it threw off a weight to me too, or something could be caught in the blower wheel. Maybe it only happens at a certain rpm. Because of my inquisitive nature, I've noticed over the years that some manufacturers have wheels that run much truer than others when new. I have a habit of spinning them with my hand and making this observation the second I lift the box off. Weird I know, but just can't help myself it's part of my nature. Check for something being caught in the wheel, then start and stop it to see if the vibes are synonymous with blower function. Good luck!