Pulling vacuum and a thud noise

[VAND]

99 Chevy k1500 truck
I was pulling vacuum, gauge at -29 and I hear a thud noise, vacuum gauge vacuum drops then comes right back up to -29. It's holding vacuum.

Could it have been the dessicant inside the acc/drier? Should I replace the acc/drier just to be on the safe side?

Recent work, installed a new orifice tube.

Is there anything I should check further before charging the system?

Is this something I should be worried about?
Thanks for your help.

[Cornbinder89]

It looks to me, with the vacuum dropping (absolute pressure rising) that you have moisture boiling off. I would change the accumulator/drier after having pulled a vacuum that was steady. In otherwords, get all the moisture you can out before changing the drier, the pull down again and charge, any moisture left will be handled by the drier bed.

[Tom Greenleaf]

Agree and no clue right now on that "THUD?" Must be inside the largest item as Cornbinder89 said just toss that accumulator this time cut it open IMO I'd want to see what the heck the inside looks like?

It doesn't fit this scene but know the actuators for these are electric and the doors that move from one request to another totally can make noise. Some were reported stuck from their extreme closed position (just reported not by me) from just disconnecting a battery! None of that has a thing to do with holding a vacuum so just a tidbit to know has happened,