Philips/Fluke PM 2525 multimeter - help with strange noise

[OpenCedar]

I have a Philips/Fluke PM 2525 multimeter which is making an odd noise. I have identified it happening twice:

- Once when it powers on

- Every time you switch from AC to DC measurement (perhaps more I have not discovered)

The noise is mechanical, best described as the sound a fish tank pump may make for up to about a second before it stops and operation seems normal.

Has anyone seen a similar issue and can point me to the root cause?

I have attached a photo of the model in question. Many thanks!

--- Updated May 7, 2022 ---

I have an update for the community:

I decided to open it.

It has a rotary wheel inside, similar to a handheld, but with a motor. This is what was responsible for the noise.

Has anyone lubricated anything similar? I have watch oil I was considering after trying to give it a wash with 99% alcohol.

 

[OpenCedar]

And a final update in the event anyone searches for this Fluke or Philips series:

The gears inside are just hard plastic and rough, and fitted about as well as the gears in a kid's toy. It must work, but wow, the engineers didn't think of this? If I had the 3d printing skills it would be cool to fashion a mod, but I don't.

If you are worried about this noise, it's a way it's built. I put a bit of watch oil on the gear but it did little to nothing.