Hi,

I recently purchased a Chamberlain B4603TC replacement garage door opener from Costco. There was a Liftmaster in there previously, but it looks like it was from '03 so we felt it was time and wanted to replace with a belt drive.

Anyway, I followed through the instructions and replaced it successfully while being able to re-use some of the existing hardware (mounting brackets for the motor, header bracket for the rail, etc.).

It was all working perfectly and I was testing out various things (sensors, remote openers, etc.) and then it started making a reasonably loud vibrating sound, usually when opening. I'd say it's mostly when it's pulling the door from vertical to horizontal, and probably stops about halfway along that, but it's not exact.

It stops if I push up underneath the motor unit at the side closest to the garage door. I can't figure out what exactly is vibrating, but that seems to help.

The spring (I have no idea of the age, whether it has been replaced at any point prior to us moving here in 2014) seems to be working fine. If I disengage the trolley and lift it to about halfway open (or I think about 4ft open as suggested), it stays open without issue.

When I installed it initially, I mounted at the exact same height as my previous opener, which I can only assume was installed professionally given it was Liftmaster (as opposed to Chamberlain), but I don't know for sure. There's not a lot of clearance because my garage has a finished ceiling. I'd say the angle of the rail wasn't quite as described in the instructions, so I used the 2 by 4 trick on top of the door (as recommended by Chamberlain) and then mounted the motor unit slightly lower as per those results. It made no difference to the vibrations. For now, I've moved it back to the original height because the lack of clearance from the door to the ceiling meant the door was slightly catching the rail on the way up, but it didn't appear to cause any issues.

I've tightened the various bolts: u bracket to motor unit, mounting brackets for motor to ceiling, etc. but no luck.

I've included a few videos at this link: https://drive.google.com/drive/folde...8J?usp=sharing
(Honestly the vibration isn't as obvious in the video as I'd like, but I'm hopeful you can hear it. It is annoying enough that I want to try fix it. If I can capture anything else, let me know).

I don't think there's any concern over it being safe, falling down, etc. But I'd like to stop the noise, especially since I switched from chain to belt to get it quieter.

Any ideas? I've seen recommendations of bushings (spelling?) at the bolts for the mounting brackets, but I don't know yet if that's causing the problems or if it's something else.

Thanks!