Recently we noticed our four year old Frigidaire
Affinity gas dryer started vibrating and this generally very quiet dryer was now noisy. My wife took it upon herself to clean out all of the ducting (finding a mouse nest in the process). While this was long over due, it didn't help with the vibration. I downloaded the service manual and went through the machine and found no problems. Yet the vibration persisted.
I hypothesized that if something (say a loose sock) got sucked into the squirrel cage blower (perhaps due to someone leaving the lint filter out) that this could throw the blower out of balance. The problem in checking out this theory is getting to the inlet side of the blower... They really don't make it easy to access this area of the dryer. However, if you remove the lint trap / sensor bar frame, you can just about wiggle your hand and arm down to the blower. (better yet if you have a young kid with skinny arms to reach down there...) Voilla! While we didn't find a sock in the blower, we did find a huge softball size chunk of lint. Upon removing the lint ball the vibration was completely gone!! Hooray! A nice simple no-cost fix. Hopefully, this will help someone else with a similar problem.